Use https for github sources (github deprecated insecure git)

[abrom]

Github have recently dropped support for fetching sources using the git protocol (port 9418) in a bid to prevent MITM issues.

Subsequently trying to fetch a source defined with the github option will result in:

10:27:06  bower mypackage#master                             ECMDERR Failed to execute "git ls-remote --tags --heads git://github.com/user/mypackage.git", exit code of #128 fatal: remote error:    The unauthenticated git protocol on port 9418 is no longer supported. Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.
10:27:06  
10:27:06  Additional error details:
10:27:06  fatal: remote error: 
10:27:06    The unauthenticated git protocol on port 9418 is no longer supported.
10:27:06  Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.
10:27:06  rake aborted!

This change swaps out the insecure git protocol for https in the DSL parsing.

Note of course that this would still allow someone to specify the git protocol using the git option, however given this issue is only specific to Github, that would seem perfectly reasonable.

This could do with some sort of explanation in the README, however it very much comes down to how the git content is hosted so very likely outside the scope of this project