Just merge if a recent 'bors try' succeeded

Support
#1

Hi,

I was wondering if it was possible for a bors r+ to simply merge (without running the tests) if there was a recent successful bors try and the master branch has not changed in the meantime?

This would save us some time/power in certain scenarios.

Thanks!

#2

This is a cool idea! I have no idea how difficult it would be to implement though.