Fix Mixed Content warning for external resources

[phit]

Proxying this through Nginx and got some mixed content warnings. This fixes it, not sure if this project is still active.
Either way you can easily do this by manually editing the release jar, just leaving it here for anyone that may find it useful in the future.

[FahriDevZ]

This is only used for https? I recommends using // (double slash) for http and https.

[phit]

there's no reason to ever request over http when https is available

see the big yellow box here https://www.paulirish.com/2010/the-protocol-relative-url/
and https://digital.gov/2015/08/14/secure-central-hosting-for-the-digital-analytics-program/#breaking-the-protocol-relative-url