fix diff command

diffido.py

@@ -216,7 +216,7 @@ def get_diff(id_, commit_id='HEAD', old_commit_id=None):
     logger.warn('MEHHHH %s  %s  %s' % (id_, commit_id, old_commit_id))
     def _history(id_, commit_id, old_commit_id, queue):
         os.chdir('storage/%s' % id_)
-        p = subprocess.Popen([GIT_CMD, 'commit_id', old_commit_id or '%s~' % commit_id, commit_id],
+        p = subprocess.Popen([GIT_CMD, 'diff', old_commit_id or '%s~' % commit_id, commit_id],
                              stdout=subprocess.PIPE)
         stdout, _ = p.communicate()
         queue.put(stdout)