message: build: force fetch PR in merge script
  Use `-f` when doing `git fetch` for the PR. Without
  it the `git fetch` will not overwrite what is currently
  fetched locally, in essence doing fast-forward only.
  PR Close
diff: @@ -67,7 +67,7 @@ else
  fi
  -FETCH_PR="git fetch https://github.com/angular/angular.git pull/$PR_NUMBER/head:angular/pr/$PR_NUMBER"
  +FETCH_PR="git fetch https://github.com/angular/angular.git pull/$PR_NUMBER/head:angular/pr/$PR_NUMBER -f"
  CHERRY_PICK_PR="git cherry-pick angular/pr/$PR_NUMBER~$PR_SHA_COUNT..angular/pr/$PR_NUMBER"
  REWRITE_MESSAGE="git filter-branch -f --msg-filter \"$BASEDIR/utils/github_closes.js $PR_NUMBER\" HEAD~$PR_SHA_COUNT..HEAD"
  