Update .gitmodules to use https urls

[dark64]

Recent changes in the Git protocol security on GitHub https://github.blog/2021-09-01-improving-git-protocol-security-github/ broke our build script that clones libsnark. I found that some submodules referenced in .gitmodules use the unencrypted git protocol and some use https, which produces an error The unauthenticated git protocol on port 9418 is no longer supported if the repository is cloned using the https protocol.

[AntoineRondelet]

Ah yes good catch @dark64 thanks for this. I actually updated it on https://github.com/clearmatics/libsnark/pull/37 but forgot to propagate here...

[AntoineRondelet]

@ValarDragon is there any plan to release a new version of libsnark at some point in the near future? If so, I think this PR should probably target staging for now and will hit master on the new release.

[mkumar-cognam]

we can also use git to change protocol to https using below command

git config --global url."https://".insteadOf git://