Bump suggested Ruby to 1.9.3-p551

DoS Security issue in Ruby 1.9.3-p550 and prior, described here:

https://www.ruby-lang.org/en/news/2014/11/13/ruby-1-9-3-p551-is-released/

Not a hair-on-fire kind of deal, but should update at the earliest
opportunity to avoid getting DoS'ed by a malicious target.