Docs: use https for a domain that supports it (#55)

README.md

@@ -156,7 +156,7 @@ Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at
 
-     http://www.apache.org/licenses/LICENSE-2.0
+     https://www.apache.org/licenses/LICENSE-2.0
 
 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,