Update ZenTest to 4.9.2.

=== 4.9.2 / 2013-05-29

* 2 minor enhancements:

  * Added autotest-suffix description to readme. (blowmage)
  * zentest now outputs test classes for minitest 5

=== 4.9.1 / 2013-04-18

* 2 minor enhancements:

  * Make banner more explicit about correct test file location. (rue)
  * Switched to #failed for calculating red/green hook. (bhenderson)

(taca)