* Run the checks against the git index (ie, what you're about to commit), rather than the working copy * Add the changes made by `go fmt` back to the index, so that they are included in the commit, as well as the working copy.
This was previously at https://github.com/vector-im/riot-web/blob/develop/scripts/rageshake.go, but it's not really exclusive to riot-web, and given I'm about to add some more complexity to it, I'd like for it to be in its own repo.