git_command.py utf-8 error
I've started getting this error on Sublime Text 3176 (Portable Edition) with git 2.17.1 on Windows 7.

```
'utf-8' codec can't decode byte 0x8a in position 16: invalid start byte

Traceback (most recent call last):
  File "[...]Sublime\\Data\\Installed Packages\\GitSavvy.sublime-package\\core/git_command.py", line 215, in git
    stdout, stderr = self.decode_stdout(stdout), stderr.decode()
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x8a in position 16: invalid start byte
```

The error appears on loading Sublime and prevents using GitSavvy. It was running until recently with no notable changes and updates.

diff --git a/core/git_command.py b/core/git_command.py
index 6d941341..dff3579c 100755
--- a/core/git_command.py
+++ b/core/git_command.py
@@ -212,7 +212,7 @@ class GitCommand(StatusMixin,
                 stdout, stderr = p.communicate(stdin)
 
             if decode:
-                stdout, stderr = self.decode_stdout(stdout), stderr.decode()
+                stdout, stderr = self.decode_stdout(stdout), self.decode_stdout(stderr)
 
             if show_panel and not live_panel_output:
                 initialize_panel()
@@ -236,7 +236,7 @@ class GitCommand(StatusMixin,
                     args,
                     stdin,
                     self.decode_stdout(stdout),
-                    stderr.decode(),
+                    self.decode_stdout(stderr),
                     end - start
                 )
 
@@ -266,7 +266,7 @@ class GitCommand(StatusMixin,
         silent_fallback = self.savvy_settings.get("silent_fallback")
         try:
             return stdout.decode()
-        except UnicodeDecodeError as unicode_err:
+        except UnicodeDecodeError:
             try:
                 return stdout.decode("latin-1")
             except UnicodeDecodeError as unicode_err:
['core/git_command.py']