Update references to CC0 URI to https for consistency

[sarahpearson]

Describe the bug
Someone reported through Freshdesk that there are inconsistencies in how CC lists the URI for CC0. Sometimes it is http and sometimes https. They found this confusing.

To Reproduce
For example, the cc0 chooser (https://creativecommons.org/choose/zero/) shows the URI as "http://creativecommons.org/publicdomain/zero/1.0/" but the preview version of it shows the https-URI as anchor link under the license banner

The person also identified that https://wiki.creativecommons.org/wiki/License_Properties and
https://creativecommons.org/publicdomain/zero/1.0/rdf include the http version of the URI.

Expected behavior
The identical URI should be used everywhere in CC's materials/resources to avoid any confusion. I believe the https version is the most up-to-date one and should be considered the canonical.

[TimidRobot]

• I updated https://wiki.creativecommons.org/wiki/License_Properties
• RDF issue is tracked by License URIs use http uri scheme, not https · Issue #7 · creativecommons/cc.licenserdf