Update link to Font Awesome

They have a shiny new site for v5 - https://fontawesome.com/

docs/4.0/migration.md

@@ -79,7 +79,7 @@ Here are the big ticket items you'll want to be aware of when moving from v3 to
 - **Dropped the Glyphicons icon font.** If you need icons, some options are:
   - the upstream version of [Glyphicons](https://glyphicons.com/)
   - [Octicons](https://octicons.github.com/)
-  - [Font Awesome](http://fontawesome.io/)
+  - [Font Awesome](https://fontawesome.com/)
   - See the [Extend page]({{ site.baseurl }}/docs/{{ site.docs_version }}/extend/icons/) for a list of alternatives. Have additional suggestions? Please open an issue or PR.
 - **Dropped the Affix jQuery plugin.**
   - We recommend using `position: sticky` instead. [See the HTML5 Please entry](http://html5please.com/#sticky) for details and specific polyfill recommendations. One suggestion is to use an `@supports` rule for implementing it (e.g., `@supports (position: sticky) { ... }`)/