use https to avoid host key verification problem

[stephaniewang526]

Using ssh might result in host key verification failure unless specifically configured.

Host key verification failed.
fatal: Could not read from remote repository.

Also, this makes it consistent with the duckdb submodule (above) where https is used.

[gdubya]

This would be useful for my work environment where cloning using the git protocol from github is not allowed.

[samansmink]

thanks @stephaniewang526!