fix markdown formatting in RULES.md
fix markdown formatting in RULES.md

A previous commit broke the formatting on this line: https://github.com/feross/standard/commit/e765b91c878ee454300dc3a9d76c41472d416b0c#commitcomment-16730715
JedWatson/happiness,JedWatson/happiness,SimenB/standard,LinusU/standard,SimenB/standard,feross/standard,feross/standard,standard/standard,standard/standard,jasonpincin/standard,LinusU/standard