data-source-url is getting sent as a hostname rather than a full url

[stevector]

This command is sending a hostname like mu-my-awesome-site.pantheonsite.io rather than a full url like https://mu-my-awesome-site.pantheonsite.io, which is what we have in examples. I think we should be sending the https:// too in the param name.

This difference isn't breaking anything as long as the Gatsby site getting triggered knows if the incoming param will have https:// or not. But it's worth picking one and aligning this plugin with the orb examples.