Using hub to fork Homebrew and push a branch we've just created to this
fork will be rejected by GitHub because the push is coming from a
shallow repository. Ensure that Homebrew is unshallowed before that.
[ci skip]
The script handles bumping up the version number, committing, tagging
and updating the Homebrew formula. The last step requires `hub` to be
installed in order to submit a pull request to Homebrew.
/cc @sferik @hsbt
[ci skip]