Prepare bpm-release for the main default branch

CONTRIBUTING.md

@@ -6,7 +6,7 @@ request](https://help.github.com/articles/using-pull-requests).
 The `bpm-release` repository is a [BOSH](https://github.com/cloudfoundry/bosh)
 release for BPM.
 
-Changes are via pull request (PR) to the master branch of its repository. 
+Changes are via pull request (PR) to the main branch of its repository.
 
 Please verify your changes before submitting the PR by following the
 [Testing](#testing) section below.

ci/pipeline.yml

@@ -27,7 +27,7 @@ resources:
 - name: bpm-release
   type: git
   source:
-    branch: master
+    branch: main
     private_key: ((github_deploy_key_bpm-release.private_key))
     uri: git@github.com:cloudfoundry/bpm-release.git
 
@@ -122,7 +122,7 @@ resources:
   type: git
   source:
     uri: git@github.com:cloudfoundry/bpm-release
-    branch: master
+    branch: main
     paths: [ci/Dockerfile]
     private_key: ((github_deploy_key_bpm-release.private_key))