Remove NPM ShellJS and use Node's child_process.execSync

[jasongitmail]

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https://nodejs.org/api/child_process.html#child_process_child_process_execsync_command_options

[jasongitmail]

If we're able to switch entirely to this built in module, then we remove one dependency, which is nice. But we may be using ShellJS' features that make it easier/cleaner to keep using it in some instances. So it might not be worth doing this. Something to look into.