Bump to p547 to fix a regression in p545

In my excitement of landing #3281 I didn't check to see if there was a
newer Ruby available. Turns out, p547 was released on May 16, and fixes
a regression regarding OpenSSL.

Announcement:

https://www.ruby-lang.org/en/news/2014/05/16/ruby-1-9-3-p547-released/

Sorry about the shuffle.
Land #3410, 1.9.3-p547 for .ruby-version