Update ruby-xz to 0.2.3.

== 0.2.3 (2015-12-29)

* *Fix* documentation of XZ module (a :nodoc: was causing havoc
  in the XZ module so it appeared to have no methods).
* No other changes this release.

== 0.2.2 (2015-12-27)

* *Add* XZ.disable_deprecation_notices
* *Deprecate* use of XZ::StreamReader.open with an IO argument
* *Deprecate* use of XZ::StreamReader.new with a filename argument
* *Deprecate* use of XZ::StreamWriter.open with an IO argument
* *Deprecate* use of XZ::StreamWriter.new with a filename argument
* *Deprecate* nonautomatic IO close in XZ::StreamReader#close
* *Deprecate* nonautomatic IO close in XZ::StreamWriter#close
* *Fix* incompatibility with Resolv.getaddress() in Ruby 2.2 (Ticket #13
  by Ken Simon)
* Goal of these deprecations is to sync the API with Ruby窶冱 own
  Zlib::GzipWriter and Zlib::GzipReader mostly.
* Add required versions to gemspec.
* Comment format cleanup, results in better docs.
* Internal code cleanup
* Add more tests.


(taca)