use_github_release() can tag the wrong commit

[davidchall]

The use_github_release() function creates a draft GitHub Release using the corresponding GitHub API. However, it doesn't set the target_commitish field and so GitHub uses the default branch (usually master).

There are situations where your local HEAD doesn't correspond to the remote default branch. For example, when releasing patches from a non-master branch. In this case, use_github_release() checks that local commits have been pushed to the remote, but then tags the wrong commit. I think this function should probably be tagging the most recent local commit.