Modifying submodules to use https instead of git for git URL

Currently submodules are using the git protocol. Git protocol is blocked
by certain corporate networks which makes it difficult to sync the submodules.

Replacing the git protocol with https in order to sync the submodules.

Fixes #333.
Merge pull request #350 from vivekgalatage/master

Support for https:// protocol for git submodules for servo