Using https:// link on README.

Author: tallesl

README.md

@@ -36,6 +36,6 @@ Check the [issues]!
 Check the [help wanted] label!
 
 [master branch]: https://github.com/fluentscheduler/FluentScheduler
-[documentation]: http://fluentscheduler.github.io
+[documentation]: https://fluentscheduler.github.io
 [issues]:        https://github.com/fluentscheduler/FluentScheduler/issues
 [help wanted]:   https://github.com/fluentscheduler/FluentScheduler/labels/help%20wanted