Update mochajs documentation link.

sky/HACKING.md

Index: sky/HACKING.md
diff --git a/sky/HACKING.md b/sky/HACKING.md
index 94977af6a4654c6578eaa10783d9728b719bb532..442b406f2a98112f1c78cb5a1da1bbab506086e6 100644
--- a/sky/HACKING.md
+++ b/sky/HACKING.md
@@ -31,7 +31,7 @@ Writing tests
 -------------
 
 * Import ``resources/mocha.html`` and ``resources/chai.html``
-* Write tests in [mocha format](http://visionmedia.github.io/mocha/#getting-started) and use [chai asserts](http://chaijs.com/api/assert/):
+* Write tests in [mocha format](http://mochajs.org/#getting-started) and use [chai asserts](http://chaijs.com/api/assert/):
 ```html
 describe('My pretty test of my subject', function() {
   var subject = new MySubject();