I have a pretty specific use of js-buy-sdk because:
1. I don't use any transpiler as a bridge between my source code and the distribution. That means I can't just install the library
2. I use ES6 style imports and app development philosophy in general.
So my question is, how can I access the Client object if I included the API in the form of <script src="http://sdks.shopifycdn.com/js-buy-sdk/v2/latest/index.umd.min.js"></script>
