Notify the user to push after merging a feature.

Fixes #72.

We do this on `hotfix merge` so why not on `feature merge`?
feature.rb: don't advise to push twice

Cause they don't need to.
Merge notify-push-after-merge (#73) into master

Notify the user to push after merging a feature.

Fixes #72.

We do this on `hotfix merge` so why not on `feature merge`?