Use https:// for submodule repository address

The address with git@github.com:... can't download by environment without
github ssh rsa key.

Submodule with https:// address can be wasy download, but not convinence for
upload/push, this can be fixed by add a pushurl in remote section of
submodule's git config file, at local development environment.

@link https://stackoverflow.com/questions/16080415
@link http://git-scm.com/docs/git-push