readme: update some links (#548)

Author: atouchet

README.md

@@ -64,8 +64,8 @@ fn main() {
 
 Licensed under either of
 
-- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://apache.org/licenses/LICENSE-2.0)
-- MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
+- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or https://apache.org/licenses/LICENSE-2.0)
+- MIT license ([LICENSE-MIT](LICENSE-MIT) or https://opensource.org/licenses/MIT)
 
 # Contribution