Update index.html

Author: tarelli

index.html

@@ -199,7 +199,7 @@ <h1>Open source visualization and simulation platform.</h1>
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 				    <br/>
 				</p>
-				<a class="btn btn-large btn-warning" href="http://geppetto.org" target="_blank">Learn more</a>
+				<a class="btn btn-large btn-warning" href="http://www.geppetto.org" target="_blank">Learn more</a>
 				<a class="btn btn-large btn-primary" href="https://github.com/openworm/org.geppetto/releases"
 				   target="_blank">Download</a>
 				<a class="btn btn-large btn-primary" href="http://git.geppetto.org" target="_blank">Sources</a>