Docs: Update a link to the WebKit test case reduction guide

The URL has change and it uses HTTPS now.

Author: mgol

CONTRIBUTING.md

@@ -55,7 +55,7 @@ Sometimes, bugs are introduced in newer versions of jQuery that do not exist in
 
 ### Reduce, reduce, reduce!
 
-When you are experiencing a problem, the most useful thing you can possibly do is to [reduce your code](http://webkit.org/quality/reduction.html) to the bare minimum required to reproduce the issue. This makes it *much* easier to isolate and fix the offending code. Bugs that are reported without reduced test cases take on average 9001% longer to fix than bugs that are submitted with them, so you really should try to do this if at all possible.
+When you are experiencing a problem, the most useful thing you can possibly do is to [reduce your code](https://webkit.org/test-case-reduction/) to the bare minimum required to reproduce the issue. This makes it *much* easier to isolate and fix the offending code. Bugs that are reported without reduced test cases take on average 9001% longer to fix than bugs that are submitted with them, so you really should try to do this if at all possible.
 
 ## jQuery Core Style Guide