If you're familiar with bbatsov/ruby-style-guide, you can immediately bbatsov-ize the files you changed in a (current) feature branch:
git diff origin/master --name-status | awk '{print $2}' | xargs rubocop --auto-correct
That roughly transates to: get all changed files in the current feature branch and run each file through rubocop, autocorrecting (modifying) the files if possible.
I recommend saving the changes in a separate commit for easier code reviews.