README remove gitter badge

README.md

@@ -2,7 +2,7 @@
 
 [![Releases](https://img.shields.io/github/release/PX4/Firmware.svg)](https://github.com/PX4/Firmware/releases) [![DOI](https://zenodo.org/badge/22634/PX4/Firmware.svg)](https://zenodo.org/badge/latestdoi/22634/PX4/Firmware) [![Build Status](https://travis-ci.org/PX4/Firmware.svg?branch=master)](https://travis-ci.org/PX4/Firmware) [![Coverity Scan](https://scan.coverity.com/projects/3966/badge.svg?flat=1)](https://scan.coverity.com/projects/3966?tab=overview)
 
-[![Slack](https://px4-slack.herokuapp.com/badge.svg)](http://slack.px4.io) [![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/PX4/Firmware?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+[![Slack](https://px4-slack.herokuapp.com/badge.svg)](http://slack.px4.io)
 
 This repository holds the [PX4 Pro](http://px4.io) flight control solution for drones, with the main applications located in the [src/modules](https://github.com/PX4/Firmware/tree/master/src/modules) directory. It also contains the PX4 Drone Middleware Platform, which provides drivers and middleware to run drones.