cmd/gerritbot: use https:// for cloning
cmd/gerritbot: use https:// for cloning

GitHub has shut down git:// as of yesterday; see
https://github.blog/2021-09-01-improving-git-protocol-security-github/.

Looking at https://api.github.com/repos/golang/go, the clone URL should
be better.

Fixes golang/go#51722.

Change-Id: I629d6c8338df1c5633ae4a6a641d57be02e90fc2
Reviewed-on: https://go-review.googlesource.com/c/build/+/393375
Trust: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
Run-TryBot: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/build,golang/build,golang/build,golang/build