Update `rufo-mode.el` name
Update `rufo-mode.el` name

At the recommendation of the [melpa](https://github.com/melpa/melpa) maintainer, I've renamed my package to `rufo.el`. 

Also, I'm willing to remove the :construction:, since I feel ready for people to use the plugin.
ruby-formatter/rufo,ruby-formatter/rufo,ruby-formatter/rufo