githooks: fix push reject when develop is directly based on master

The issue this fixes is that git reports same commit as being ancestor of itself. It kind of makes sense but it breaks check if branch is based on master or develop. In such case the common base between develop and target branch and master and target branch is the same.

This changes the logic. Because git merge-base does effectively the operation of 'less than or equal' we have to swap compare order and negate the result. This way we get effectively the 'less than' operation.