Fix coveralls badge

Author: asottile

README.md

@@ -1,5 +1,5 @@
 [![Build Status](https://travis-ci.org/pre-commit/pre-commit.svg?branch=master)](https://travis-ci.org/pre-commit/pre-commit)
-[![Coverage Status](https://img.shields.io/coveralls/pre-commit/pre-commit.svg?branch=master)](https://coveralls.io/r/pre-commit/pre-commit)
+[![Coverage Status](https://coveralls.io/repos/github/pre-commit/pre-commit/badge.svg?branch=master)](https://coveralls.io/github/pre-commit/pre-commit?branch=master)
 [![Build status](https://ci.appveyor.com/api/projects/status/mmcwdlfgba4esaii/branch/master?svg=true)](https://ci.appveyor.com/project/asottile/pre-commit/branch/master)
 
 ## pre-commit