Fix README badges (#844)

README.md

@@ -1,8 +1,8 @@
 [![Gem Version](https://badge.fury.io/rb/overcommit.svg)](https://badge.fury.io/rb/overcommit)
-[![Build Status](https://github.com/sds/overcommit/actions/workflows/tests.yml/badge.svg?branch=master)](https://github.com/sds/overcommit/actions/workflows/tests.yml/badge.svg?branch=master)
-[![Coverage Status](https://coveralls.io/repos/github/sds/overcommit/badge.svg?branch=master)](https://coveralls.io/github/sds/overcommit?branch=master)
+[![Build Status](https://github.com/sds/overcommit/actions/workflows/tests.yml/badge.svg?branch=main)](https://github.com/sds/overcommit/actions/workflows/tests.yml/badge.svg?branch=main)
+[![Coverage Status](https://coveralls.io/repos/github/sds/overcommit/badge.svg?branch=main)](https://coveralls.io/github/sds/overcommit?branch=main)
 [![Maintainability](https://api.codeclimate.com/v1/badges/5da42f7f365e5fef6b4c/maintainability)](https://codeclimate.com/github/sds/overcommit/maintainability)
-[![Inline docs](http://inch-ci.org/github/sds/overcommit.svg?branch=master)](http://inch-ci.org/github/sds/overcommit)
+[![Inline docs](http://inch-ci.org/github/sds/overcommit.svg?branch=main)](http://inch-ci.org/github/sds/overcommit)
 
 <p align="center">
   <img src="https://raw.githubusercontent.com/sds/overcommit/master/logo/horizontal.png" width="65%" alt="Overcommit Logo"/>