Merge pull request #16222 from yuan3y/patch-1

fix dead link: reduced text cases

CONTRIBUTING.md

@@ -66,7 +66,7 @@ Guidelines for bug reports:
    latest `master` or development branch in the repository.
 
 3. **Isolate the problem** — ideally create a [reduced test
-   case](http://css-tricks.com/6263-reduced-test-cases/) and a live example.
+   case](https://css-tricks.com/reduced-test-cases/) and a live example.
    [This JS Bin](http://jsbin.com/lefey/1/edit?html,output) is a helpful template.