feat(git): Omit git info when git isnt installed

Addresses this comment: #174 (comment)

Previously, git info was omitted if git was installed but the .git directory was missing.
This fix will also omit git info in case git itself is missing (unless, of course, the environment args are there).

coveralls/git.py

@@ -74,7 +74,7 @@ def git_info():
         remotes = [{'name': line.split()[0], 'url': line.split()[1]}
                    for line in run_command('git', 'remote', '-v').splitlines()
                    if '(fetch)' in line]
-    except CoverallsException as ex:
+    except (CoverallsException, EnvironmentError):
         # When git is not available, try env vars as per Coveralls docs:
         # https://docs.coveralls.io/mercurial-support
         # Additionally, these variables have been extended by GIT_URL and
@@ -94,7 +94,8 @@ def git_info():
         }]
         if not all(head.values()):
             log.warning('Failed collecting git data. Are you running '
-                        'coveralls inside a git repository?', exc_info=ex)
+                        'coveralls inside a git repository? Is git installed?',
+                        exc_info=True)
             return {}
 
     return {