브랜치 삭제로 인한 PR Close, Reopen 방법

• git push -f origin 0abcdef:my-feature #pushing the old commit the PR has been closed with
  (또는 git push -f origin 0abcdef:refs/head/my-feature)
• Reopen the PR.
• git push -f origin 1234567:my-feature #pushing the latest commit

[참고] https://gist.github.com/robertpainsi/2c42c15f1ce6dab03a0675348edd4e2c