Add latest rubies to ci_environment

This adds ruby 2.1.4, 2.0.0-p594, 1.9.3-p550 to all the machines.  It
additionally removes 2.1.3, as this has only just been added, and isn't
used by anything yet.

These new releases include a change to the openssl library to disable
insecure SSL/TLS options in response to POODLE[1].  They also include a
fix for a REXML DoS vulnerability[2]

[1] https://www.ruby-lang.org/en/news/2014/10/27/changing-default-settings-of-ext-openssl/
[2] https://www.ruby-lang.org/en/news/2014/10/27/rexml-dos-cve-2014-8080/