Finish hotfix should checkout the master branch before tagging

[Etherion]

In some situations, the tag after finishing a hotfix is not placed on the master branch commit, but is on the develop branch commit as described in #416 Added a checkout of the master branch before tagging, identically to how the finish release script is doing.

[ChrisJStone]

I'm in the process of updating gitflow. If you could kindly resubmit your pull request against my fork here as it appears this fork is no longer being updated.