Parse Git Revision via Subprocess Call

For some reason Raven doesn't seem to be retrieving the Git revision as
intended, so let's revert it back to the way it was working with before.

Fixes #137

Author: liam-middlebrook

conditional/__init__.py

@@ -17,10 +17,10 @@
 app.config.from_pyfile(config)
 app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
 
-try:
-    app.config["GIT_REVISION"] = fetch_git_sha(app.config["ROOT_DIR"])[:7]
-except (InvalidGitRepository, KeyError):
-    app.config["GIT_REVISION"] = "unknown"
+app.config["GIT_REVISION"] = subprocess.check_output(['git',
+                                                      'rev-parse',
+                                                      '--short',
+                                                      'HEAD']).decode('utf-8').rstrip()
 
 
 db = SQLAlchemy(app)