Rename master branch to main

Author: mmassaki

.github/workflows/actions.yml

@@ -4,7 +4,6 @@ on:
   pull_request:
   push:
     branches:
-      - master
       - main
 
 jobs:

README.md

@@ -15,7 +15,7 @@ Very likely you want to try out your changes with the use of ZAT. See [ZAT](http
 This project uses Rspec, which can be run with `bundle exec rake`.
 
 ## Contribute
-* Put up a PR into the master branch.
+* Put up a PR into the main branch.
 * CC and get two +1 from @zendesk/wattle.
 
 ### Releasing a new version