Rename master branch to main

Author: oschulz

.github/workflows/ci.yml

@@ -3,7 +3,7 @@ name: CI
 on:
   push:
     branches:
-      - master
+      - main
       - dev
       - 'releases/**'
     tags: '*'

README.md

@@ -3,8 +3,8 @@
 [![Documentation for stable version](https://img.shields.io/badge/docs-stable-blue.svg)](https://oschulz.github.io/ForwardDiffPullbacks.jl/stable)
 [![Documentation for development version](https://img.shields.io/badge/docs-dev-blue.svg)](https://oschulz.github.io/ForwardDiffPullbacks.jl/dev)
 [![License](http://img.shields.io/badge/license-MIT-brightgreen.svg?style=flat)](LICENSE.md)
-[![Build Status](https://github.com/oschulz/ForwardDiffPullbacks.jl/workflows/CI/badge.svg?branch=master)](https://github.com/oschulz/ForwardDiffPullbacks.jl/actions?query=workflow%3ACI)
-[![Codecov](https://codecov.io/gh/oschulz/ForwardDiffPullbacks.jl/branch/master/graph/badge.svg)](https://codecov.io/gh/oschulz/ForwardDiffPullbacks.jl)
+[![Build Status](https://github.com/oschulz/ForwardDiffPullbacks.jl/workflows/CI/badge.svg?branch=main)](https://github.com/oschulz/ForwardDiffPullbacks.jl/actions?query=workflow%3ACI)
+[![Codecov](https://codecov.io/gh/oschulz/ForwardDiffPullbacks.jl/branch/main/graph/badge.svg)](https://codecov.io/gh/oschulz/ForwardDiffPullbacks.jl)
 
 ForwardDiffPullbacks implements pullbacks compatible with
 [ChainRulesCore](https://github.com/JuliaDiff/ChainRulesCore.jl) that are calculated via