fixing bug in ga variable name

Author: andreasprlic

_includes/footer.html

@@ -27,4 +27,4 @@
 </footer>
 
 <script src="http://www.google-analytics.com/urchin.js" type="text/javascript"></script>
-<script type="text/javascript">_uacct = "{{ google_analytics }}";urchinTracker();</script>
+<script type="text/javascript">_uacct = "{{ site.google_analytics }}";urchinTracker();</script>