📦 NEW: Add lodash dependency (#143)

* Add lodash dependency

I think this should fix #133.

`window.lodash` is already present in Gutenberg. 
`window._` is underscore. 
If you import `lodash` in the code, it will override `window._` with lodash, which will cause weird bugs in totally unrelated places. 

Adding lodash here will prevent webpack from including `lodash` in the output, so it won't cause any conflicts. 

### How to test this
#133 only happend on my system, if I installed some other plugins. The easiest way to reproduce it, is to install the `TinyMCE Advanced` plugin. 

In your block code: 
Add `import { compose } from "@wordpress/compose";` to one of the JavaScript files.

`@wordpress/compose` exports `flowRight` from `lodash` as `compose`, so it imports `lodash`. 
This will cause lodash to be included in your build. 




I created a repository to show this: https://github.com/martinstuecklschwaiger/gutenberg-example

* 🐛 FIX: Grammar

Author: martinstuecklschwaiger

packages/cgb-scripts/config/externals.js

@@ -41,6 +41,7 @@ const externals = [
 		react: 'React', // React itself is there in Gutenberg.
 		jquery: 'jQuery', // import $ from 'jquery' // Use the WordPress version after enqueuing it.
 		'react-dom': 'ReactDOM',
+		lodash: 'lodash', // Lodash is there in Gutenberg.
 	}
 );