DOC: update version number

Author: tacaswell

versions.html

@@ -2,7 +2,7 @@
 
 <ul>
   <li><a href="/devdocs/index.html">2.x</a> Latest git master (unstable)</a></li>
-  <li><a href="/1.5.0/index.html">1.5.0</a> Latest stable version..</a></li>
+  <li><a href="/1.5.1/index.html">1.5.1</a> Latest stable version..</a></li>
   <li><a href="/1.4.3/index.html">1.4.3</a> Previous stable version.</a></li>
   <li><a href="/1.3.1/index.html">1.3.1</a> Older stable version.</a></li>
 </ul>