Oh good, another Ruby version bump

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.
Adds new TFTP file names, submitted by Chris McNab
Land #4216, @hmoore-r7 additions to the tftp dictionary

* Changes originally submitted by Chris McNab
Land #4211, Ruby version bump