add https to contributor covenant link

README.md

@@ -48,7 +48,7 @@ To install this gem onto your local machine, run `bundle exec rake install`. To
 
 To update the data included in the gem, just run `bundle exec rake update` and make a pull request with the changes. This will pull the latest data from [OpenFlights](http://openflights.org).
 
-Bug reports and pull requests are welcome on GitHub at https://github.com/timrogers/airports. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [Contributor Covenant](contributor-covenant.org) code of conduct.
+Bug reports and pull requests are welcome on GitHub at https://github.com/timrogers/airports. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [Contributor Covenant](https://contributor-covenant.org) code of conduct.
 
 ## Acknowledgements