WIP: using sha instead of ref to avoid branch name confusion

Author: Xin Zhang

Diff for: assets/lib/in.rb

@@ -19,7 +19,7 @@ def ref
 
 pr = Octokit.pull_request(input['source']['repo'], input['version']['pr'])
 id = pr['number']
-branch_ref = pr['head']['ref']
+branch_ref = pr['head']['sha']
 
 system("git clone --depth 1 #{uri} #{destination} 1>&2")