Updated code of conduct (#4136)

* Updated code of conduct

Link to homepage and version are updated from http to https as [Hyper Text Transfer Protocol Secure].
's' is suffixed to http to make the secure link so that it is not considered as a mallacious spam link by any browser.

* Update CODE_OF_CONDUCT.md

All links are updated up to date now.

CODE_OF_CONDUCT.md

@@ -44,7 +44,7 @@ incident.
 
 This Code of Conduct is adapted from the [Contributor Covenant][homepage],
 version 1.3.0, available at
-[http://contributor-covenant.org/version/1/3/0/][version]
+[https://contributor-covenant.org/version/1/3/0/][version]
 
-[homepage]: http://contributor-covenant.org
-[version]: http://contributor-covenant.org/version/1/3/0/
+[homepage]: https://contributor-covenant.org
+[version]: https://contributor-covenant.org/version/1/3/0/