jruby: 1.7.12 -> 1.7.20.1

Security release which only updates Rubygems to version 2.4.8. Rubygems 2.4.8
addresses CVE-2015-1855 to resolve some problems with wildcard matching of
hostnames.

See following entry for more information:
http://jruby.org/2015/06/10/jruby-1-7-20-1.html