I've observed that you have a dependency on micromatch npm package which pulls in additional trivial packages like nanomatch, is-odd, is-even and is-number. The only place you're using this module is in the /lib/optimize/SideEffectsFlagPlugin.js which should be trivial to implement in pure JS.

return mm.isMatch(moduleName, flagValue, {
				matchBase: true
});

I hope you'll do it and remove this dependency soon. I also hope you understand that adding dependencies for trivial functionality like this is a worst practice presently plaguing the javascript world and the idea of "don't repeat yourself" is being carried too far with packages like is-odd and is-even.