As the number of privacy-preserving analytics options proliferates,
it no longer makes sense to support specific solutions provided by
ad-tracking corporations.
This replaces all `http://` and `//:` links with `https:`. The protocol-
relative URL scheme is now deemed to be an anti-pattern. There are
security advantages to using HTTPS, and there are no significant
performance concerns.
In short, if the asset we need is available via HTTPS, then that asset
should always be loaded via HTTPS.
Fixes#1736
