Updated Mozilla localForage link (#665)

Old link was broken

Author: paulocoghi

README.md

@@ -68,7 +68,7 @@ Companies Using Slate
 * [NASA](https://api.nasa.gov)
 * [IBM](https://docs.cloudant.com/api.html)
 * [Sony](http://developers.cimediacloud.com)
-* [Mozilla](http://mozilla.github.io/localForage/)
+* [Mozilla](http://localforage.github.io/localForage/)
 * [Best Buy](https://bestbuyapis.github.io/api-documentation/)
 * [Travis-CI](https://docs.travis-ci.com/api/)
 * [Greenhouse](https://developers.greenhouse.io/harvest.html)