Fix Christchurch link (#81)

Since we've updated our site, the old domain no longer works. Ideally,
we'd support both CNAMES on GH pages, but I don't think that's possible.
Perhaps the ruby.org.nz domain administrator can redirect to ruby.nz?

index.html

@@ -57,7 +57,7 @@ <h2>Local Meetups</h2>
       WellRailed: Wellington's Ruby on Rails Community Group
     </li>
     <li>
-      <a href="http://christchurch.ruby.org.nz">Christchurch</a>:
+      <a href="http://christchurch.ruby.nz">Christchurch</a>:
       Super friendly group of programmers meeting monthly to discuss all things about the Ruby programming language.
     </li>
   </ul>