Log Message:
Update ruby-xz to 0.2.1.

0.2.1 (2014-02-08)

* Build the gem properly on Ruby 2.0+ (PR #8 by Nana Sakisaka (saki7))
* Release the GIL when interfacing with liblzma (PR #7 by Lars Christensen
* (larsch))

0.2.0 (2013-06-23)

* Fix #6 (errors on JRuby) by Ben Nagy
* Remove 1.8 compatibility