Add Seattle.rb

[MikeRogers0]

Group: http://www.seattlerb.org/

They appear to be super active, but they don't appear to have a meetup page so I can't pull in their events.

Requirements

• Add them to the src/_data/groups.yml file
• Figure out a way to pull in their events, e.g. a new parser similar to what I've already written.
  • Their site is open source https://github.com/seattlerb/seattlerb.org so there might be some hints in there.
  • https://twitter.com/seattlerb - They appear to have some automation going on here to post the events