Merge typo-in-test_irc-6392: Fix typo in docstring in twisted.words.test.test_irc.

Author: Infinity
Reviewers: tom.prince
Fixes: #6392

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@37850 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb