Add Slack badge, remove fuzzit badge (#1712) (#1713)

README.md

@@ -1,6 +1,10 @@
 # grpc-gateway
 
-[![release](https://img.shields.io/github/release/grpc-ecosystem/grpc-gateway.svg?style=flat-square)](https://github.com/grpc-ecosystem/grpc-gateway/releases) [![CircleCI](https://img.shields.io/circleci/project/github/grpc-ecosystem/grpc-gateway/master.svg?style=flat-square)](https://circleci.com/gh/grpc-ecosystem/grpc-gateway) [![fuzzit](https://app.fuzzit.dev/badge?org_id=grpc-gateway)](https://app.fuzzit.dev/orgs/grpc-gateway/dashboard) [![coverage](https://img.shields.io/codecov/c/github/grpc-ecosystem/grpc-gateway/master.svg?style=flat-square)](https://codecov.io/gh/grpc-ecosystem/grpc-gateway) [![license](https://img.shields.io/github/license/grpc-ecosystem/grpc-gateway.svg?style=flat-square)](LICENSE.txt)
+[![release](https://img.shields.io/github/release/grpc-ecosystem/grpc-gateway.svg?style=flat-square)](https://github.com/grpc-ecosystem/grpc-gateway/releases)
+[![CircleCI](https://img.shields.io/circleci/project/github/grpc-ecosystem/grpc-gateway/master.svg?style=flat-square)](https://circleci.com/gh/grpc-ecosystem/grpc-gateway)
+[![coverage](https://img.shields.io/codecov/c/github/grpc-ecosystem/grpc-gateway/master.svg?style=flat-square)](https://codecov.io/gh/grpc-ecosystem/grpc-gateway)
+[![license](https://img.shields.io/github/license/grpc-ecosystem/grpc-gateway.svg?style=flat-square)](LICENSE.txt)
+[![Slack](https://img.shields.io/badge/slack-%23grpc--gateway-brightgreen?style=flat-square)](https://join.slack.com/t/gophers/shared_invite/zt-gmw97q11-1OWgj2Dqsc13eqoSPwvNDQ)
 
 The grpc-gateway is a plugin of the Google protocol buffers compiler
 [protoc](https://github.com/protocolbuffers/protobuf).