Extra slash in application url when using ports for serving apps
Following the Getting Started doc, There is an extra slash `/` in the generated? URL app.
 
Something like:

```
=====> Application deployed:
       http://dokku.mydomaine.com/:27451
```

instead of 

```
=====> Application deployed:
       http://dokku.feekashowroom.com:27451
```

---

dokku report $APP_NAME
```
-----> uname: Linux dokku 5.4.0-42-generic #46-Ubuntu SMP Fri Jul 10 00:24:02 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
-----> memory:
                     total        used        free      shared  buff/cache   available
       Mem:           1939         313         138          11        1487        1456
       Swap:             0           0           0
-----> docker version:
       Client: Docker Engine - Community
        Version:           19.03.12
        API version:       1.40
        Go version:        go1.13.10
        Git commit:        48a66213fe
        Built:             Mon Jun 22 15:45:44 2020
        OS/Arch:           linux/amd64
        Experimental:      false

       Server: Docker Engine - Community
        Engine:
         Version:          19.03.12
         API version:      1.40 (minimum version 1.12)
         Go version:       go1.13.10
         Git commit:       48a66213fe
         Built:            Mon Jun 22 15:44:15 2020
         OS/Arch:          linux/amd64
         Experimental:     false
        containerd:
         Version:          1.2.13
         GitCommit:        7ad184331fa3e55e52b890ea95e65ba581ae3429
        runc:
         Version:          1.0.0-rc10
         GitCommit:        dc9208a3303feef5b3839f4323d9beb36df0a9dd
        docker-init:
         Version:          0.18.0
         GitCommit:        fec3683
-----> docker daemon info:
WARNING: No swap limit support
       Client:
        Debug Mode: true

       Server:
        Containers: 8
         Running: 2
         Paused: 0
         Stopped: 6
        Images: 13
        Server Version: 19.03.12
        Storage Driver: overlay2
         Backing Filesystem: extfs
         Supports d_type: true
         Native Overlay Diff: true
        Logging Driver: json-file
        Cgroup Driver: cgroupfs
        Plugins:
         Volume: local
         Network: bridge host ipvlan macvlan null overlay
         Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
        Swarm: inactive
        Runtimes: runc
        Default Runtime: runc
        Init Binary: docker-init
        containerd version: 7ad184331fa3e55e52b890ea95e65ba581ae3429
        runc version: dc9208a3303feef5b3839f4323d9beb36df0a9dd
        init version: fec3683
        Security Options:
         apparmor
         seccomp
          Profile: default
        Kernel Version: 5.4.0-42-generic
        Operating System: Ubuntu 20.04.1 LTS
        OSType: linux
        Architecture: x86_64
        CPUs: 1
        Total Memory: 1.894GiB
        Name: dokku
        ID: OXV3:EI46:M6YN:OEHC:MWWR:4XHR:S5HT:EJDQ:5TTC:RNRZ:O7B5:55VZ
        Docker Root Dir: /var/lib/docker
        Debug Mode: false
        Registry: https://index.docker.io/v1/
        Labels:
        Experimental: false
        Insecure Registries:
         127.0.0.0/8
        Live Restore Enabled: false

-----> sigil version: 0.6.0
-----> herokuish version:
       herokuish: 0.5.13
       buildpacks:
         heroku-buildpack-multi     v1.0.0
         heroku-buildpack-ruby      v215
         heroku-buildpack-nodejs    v171
         heroku-buildpack-clojure   v84
         heroku-buildpack-python    v169
         heroku-buildpack-java      v66
         heroku-buildpack-gradle    v31
         heroku-buildpack-scala     v87
         heroku-buildpack-play      v26
         heroku-buildpack-php       v174
         heroku-buildpack-go        v142
         buildpack-nginx            v13
-----> dokku version: dokku version 0.21.4
-----> dokku plugins:
       plugn: 0.5.0
         00_dokku-standard    0.21.4 enabled    dokku core standard plugin
         20_events            0.21.4 enabled    dokku core events logging plugin
         app-json             0.21.4 enabled    dokku core app-json plugin
         apps                 0.21.4 enabled    dokku core apps plugin
         builder-dockerfile   0.21.4 enabled    dokku core builder-dockerfile plugin
         builder-herokuish    0.21.4 enabled    dokku core builder-herokuish plugin
         buildpacks           0.21.4 enabled    dokku core buildpacks plugin
         certs                0.21.4 enabled    dokku core certificate management plugin
         checks               0.21.4 enabled    dokku core checks plugin
         common               0.21.4 enabled    dokku core common plugin
         config               0.21.4 enabled    dokku core config plugin
         docker-options       0.21.4 enabled    dokku core docker-options plugin
         domains              0.21.4 enabled    dokku core domains plugin
         enter                0.21.4 enabled    dokku core enter plugin
         git                  0.21.4 enabled    dokku core git plugin
         logs                 0.21.4 enabled    dokku core logs plugin
         network              0.21.4 enabled    dokku core network plugin
         nginx-vhosts         0.21.4 enabled    dokku core nginx-vhosts plugin
         plugin               0.21.4 enabled    dokku core plugin plugin
         postgres             1.11.5 enabled    dokku postgres service plugin
         proxy                0.21.4 enabled    dokku core proxy plugin
         ps                   0.21.4 enabled    dokku core ps plugin
         repo                 0.21.4 enabled    dokku core repo plugin
         resource             0.21.4 enabled    dokku core resource plugin
         scheduler-docker-local 0.21.4 enabled    dokku core scheduler-docker-local plugin
         shell                0.21.4 enabled    dokku core shell plugin
         ssh-keys             0.21.4 enabled    dokku core ssh-keys plugin
         storage              0.21.4 enabled    dokku core storage plugin
         tags                 0.21.4 enabled    dokku core tags plugin
         tar                  0.21.4 enabled    dokku core tar plugin
         trace                0.21.4 enabled    dokku core trace plugin
```
diff --git a/contrib/dokku-installer.py b/contrib/dokku-installer.py
index 8e76655f4..c503d2e3c 100755
--- a/contrib/dokku-installer.py
+++ b/contrib/dokku-installer.py
@@ -154,7 +154,7 @@ class GetHandler(SimpleHTTPServer.SimpleHTTPRequestHandler):
         if 'vhost' in params and params['vhost'].value == 'true':
             vhost_enable = 'true'
             with open(vhost_filename, 'w') as f:
-                f.write(params['hostname'].value)
+                f.write(params['hostname'].value.strip("/"))
             shutil.chown(vhost_filename, dokku_user, dokku_group)
         else:
             try:
@@ -165,7 +165,7 @@ class GetHandler(SimpleHTTPServer.SimpleHTTPRequestHandler):
         hostname_filename = '{0}/HOSTNAME'.format(dokku_root)
 
         with open(hostname_filename, 'w') as f:
-            f.write(params['hostname'].value)
+            f.write(params['hostname'].value.strip("/"))
 
         shutil.chown(hostname_filename, dokku_user, dokku_group)
 
['contrib/dokku-installer.py']