switched contributor-covenant.org links to https

Since the website of contributor-covenant is served over https, I changed the links to use httpS rather than http to prevent the needless redirect.

CODE_OF_CONDUCT.md

@@ -40,7 +40,7 @@ Project maintainers who do not follow or enforce the Code of Conduct in good fai
 
 ## Attribution
 
-This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 1.4, available at [http://contributor-covenant.org/version/1/4][version]
+This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 1.4, available at [https://contributor-covenant.org/version/1/4][version]
 
-[homepage]: http://contributor-covenant.org
-[version]: http://contributor-covenant.org/version/1/4/
+[homepage]: https://contributor-covenant.org
+[version]: https://contributor-covenant.org/version/1/4/