Correct more grammar.

index.html

@@ -426,7 +426,7 @@
       <a href="http://github.com/documentcloud/backbone/issues">GitHub issues page</a>,
       on Freenode IRC in the <tt>#documentcloud</tt> channel, post questions to the
       <a href="https://groups.google.com/forum/#!forum/backbonejs">Google Group</a>,
-      add pages to the a <a href="https://github.com/documentcloud/backbone/wiki">wiki</a>
+      add pages to the <a href="https://github.com/documentcloud/backbone/wiki">wiki</a>
       or send tweets to <a href="http://twitter.com/documentcloud">@documentcloud</a>.
     </p>