Had to be done manually due to matrix-discord-parser pulling in a `git:`
dependency of its own.

Signed-off-by: Andrew Ferrazzutti <andrewf@element.io>

Using Git over HTTPS instead.

Unencrypted `git://` does not seem to be supported by GitHub anymore:
https://github.blog/2021-09-01-improving-git-protocol-security-github/

This prevented the package from building on NixOS:
https://github.com/NixOS/nixpkgs/issues/165246

This makes us dependent on matrix-appservice-bridge to make use of
UserActivityTracker and BridgeBlocker, which also bumps matrix-bot-sdk
to a higher required version.