Fix CI badge, as we have switched from Travis to CircleCI

README.md

@@ -2,7 +2,9 @@
 
 >   Now with automated deploys!
 
-[![Build Status](https://travis-ci.org/glitch-soc/mastodon.svg?branch=master)](https://travis-ci.org/glitch-soc/mastodon)
+[![Build Status](https://img.shields.io/circleci/project/github/glitch-soc/mastodon.svg)](https://travis-ci.org/glitch-soc/mastodon)
+
+[circleci]: https://circleci.com/gh/glitch-soc/mastodon
 
 So here's the deal: we all work on this code, and then it runs on dev.glitch.social and anyone who uses that does so absolutely at their own risk. can you dig it?