Default to bumping patch version

We had an issue this morning during a deploy where we bumped the minor version on a release branch instead of the main branch.

This meant we couldn't bump the minor on the main branch because the tag existed.

The solution is to bump the patch by default so that bumps on the release branch are patch bumps then to bump the minor explicitly when we release the main branch thus tagging over the patch bump

cc @jcorbin @squamos