Do not raise a KeyError while creating a tag

sigmavirus24 · sigmavirus24 · commit a1723a6ab3b9 · 2015-11-01T14:06:32.000-06:00
diff --git a/github3/repos/repo.py b/github3/repos/repo.py
@@ -1001,7 +1001,7 @@ def create_tag(self, tag, message, sha, obj_type, tagger,
             url = self._build_url('git', 'tags', base_url=self._api)
             json = self._json(self._post(url, data=data), 201)
             if json:
-                self.create_ref('refs/tags/' + tag, json['sha'])
+                self.create_ref('refs/tags/' + tag, json.get('sha'))
         return self._instance_or_null(Tag, json)
 
     @requires_auth
