don't use ES6 syntax in a dist package

[konqi]

using ES6 syntax will cause trouble unless you transpile before use (which is something you should not be required to do in a dist package)

[shockey]

Arrow functions are well-supported (see here and here)

.....except for IE11.

So this is a good catch. Thanks @konqi!

[konqi]

I actually had trouble importing the module with webpack. It complained that the brackets () are not expected where they are. My guess is that it's a strict eslint rule that disallows arrow functions for compatibility reasons - so yeah - blame it on IE ;-)