Cloning git repo when installing a plugin doesn't fetch submodules

When installing a plugin using a git repo as the id, e.g:

cordova plugin install https://github.com/path_to_git_repo.git

The plugman helper gitclone.js doesn't retrieve using the --recursive option, so submodules are not fetched.

This is breaking our plugin as cordova is failing to find all the necessary files as specified in the plugin.xml (some of them are from a nested git submodule repo)

Relevant PR: https://github.com/apache/cordova-lib/pull/424