Remove TravisCI badge (#503)

Author: elithrar

README.md

@@ -1,7 +1,6 @@
 # gorilla/mux
 
 [![GoDoc](https://godoc.org/github.com/gorilla/mux?status.svg)](https://godoc.org/github.com/gorilla/mux)
-[![Build Status](https://travis-ci.org/gorilla/mux.svg?branch=master)](https://travis-ci.org/gorilla/mux)
 [![CircleCI](https://circleci.com/gh/gorilla/mux.svg?style=svg)](https://circleci.com/gh/gorilla/mux)
 [![Sourcegraph](https://sourcegraph.com/github.com/gorilla/mux/-/badge.svg)](https://sourcegraph.com/github.com/gorilla/mux?badge)