Fix broken contributing link

Author: deathcap

index.html

@@ -85,7 +85,7 @@ <h2>community</h2>
       <ul>
         <li>Freenode IRC: <a href="http://webchat.freenode.net/?channels=stackgl">#stackgl</a></li>
         <li>GitHub: <a href="http://github.com/stackgl">github.com/stackgl</a></li>
-        <li>Contributing: <a href="https://github.com/stackgl/contibuting">github.com/stackgl/contributing</a></li>
+        <li>Contributing: <a href="https://github.com/stackgl/contributing">github.com/stackgl/contributing</a></li>
         <li>Shader School: <a href="http://github.com/stackgl/shader-school">github.com/stackgl/shader-school</a></li>
         <li>WebGL Workshop: <a href="http://github.com/stackgl/webgl-workshop">github.com/stackgl/webgl-workshop</a></li>
       </ul>