Update index.html

index.html

@@ -232,7 +232,7 @@
 
 				<a href="https://github.com/mrdoob/three.js/">source code</a><br />
 				<a href="https://stackoverflow.com/questions/tagged/three.js">questions</a><br />
-				<a href="http://discourse.threejs.org/">forum</a><br />
+				<a href="https://discourse.threejs.org/">forum</a><br />
 				<a href="http://webchat.freenode.net/?channels=three.js">chat<br /><br />
 
 				<a href="editor/">editor</a>