Add merge_commit_sha to PullRequest model (#1562)
Add merge_commit_sha to PullRequest model (#1562)

* Add merge_commit_sha to PullRequest model

* Update MergeCommitSha summary

thedillonb/octokit.net,eriawan/octokit.net,khellang/octokit.net,adamralph/octokit.net,alfhenrik/octokit.net,shiftkey-tester/octokit.net,shiftkey-tester/octokit.net,gdziadkiewicz/octokit.net,octokit/octokit.net,gdziadkiewicz/octokit.net,alfhenrik/octokit.net,M-Zuber/octokit.net,thedillonb/octokit.net,TattsGroup/octokit.net,eriawan/octokit.net,octokit/octokit.net,TattsGroup/octokit.net,shiftkey/octokit.net,editor-tools/octokit.net,ivandrofly/octokit.net,M-Zuber/octokit.net,editor-tools/octokit.net,shiftkey/octokit.net,ivandrofly/octokit.net,khellang/octokit.net