After Quick Deploy on Heroku, App crash due to sqlalchemy
How to reproduce the behaviour
---------
Start the quick deploy to heroku
Wait for successful build and deploy
Open app and wait for crash.

**Logs** 
`sqlalchemy.exc.NoSuchModuleError: Can't load plugin: sqlalchemy.dialects:postgres`
 `celery crashed`
`Process exited with status 12021-04-23T17:02:29.297622+00:00 heroku[web.1]: State changed from up to crashed`

Apparently versions of SQLAlchemy 1.4+ require postgresql:// and do not accept postgre:// anymore.

The DATABASE_URL start with postgres:// after deployment on heroku

Your Environment
---------
Installed with the deploy to heroku from doccano's home page, built from Dockerfile.
SQLAlchemy was 1.4.7

diff --git a/backend/app/settings.py b/backend/app/settings.py
index 5df89e66..9c4d59f0 100644
--- a/backend/app/settings.py
+++ b/backend/app/settings.py
@@ -353,7 +353,12 @@ try:
     CELERY_BROKER_URL = env('CELERY_BROKER_URL')
 except EnvError:
     try:
-        CELERY_BROKER_URL = 'sqla+{}'.format(env('DATABASE_URL'))
+        # quickfix for Heroku.
+        # See https://github.com/doccano/doccano/issues/1327.
+        uri = env('DATABASE_URL')
+        if uri.startswith('postgres://'):
+            uri = uri.replace('postgres://', 'postgresql://', 1)
+        CELERY_BROKER_URL = 'sqla+{}'.format(uri)
     except EnvError:
         CELERY_BROKER_URL = 'sqla+sqlite:///{}'.format(DATABASES['default']['NAME'])
 CELERY_ACCEPT_CONTENT = ['application/json']
['backend/app/settings.py']