message: docs: remove Gitter link from README
diff: @@ -126,7 +126,6 @@ Installation & Configuration
  Resources
  -------------
  * [Mailing list](https://lists.apache.org/list.html?dev@superset.apache.org)
  -* [Gitter (live chat) Channel](https://gitter.im/airbnb/superset)
  * [Docker image](https://hub.docker.com/r/amancevice/superset/) (community contributed)
  * [Slides from Strata (March 2016)](https://drive.google.com/open?id=0B5PVE0gzO81oOVJkdF9aNkJMSmM)
  * [Stackoverflow tag](https://stackoverflow.com/questions/tagged/apache-superset)
  