githooks/pre-push: allow fast-forward of master to develop

The original check was that master can be pushed only with develop branch. It is what we mostly want but there are cases when we do not update develop and only master that are valid as well. The example of such operation is merge of develop to master, which is always fast-forward due to our workflow.

This halts push only if master commit is not ancestor of develop instead of halting it always when develop is not being updated.