ES5 transpilation

[mykeels]

Hello, awesome work here ...

I referenced node-excel-export in my code, and my script breaks on IE11, in index.js where an arrow function is used.

I use babel, but it won't transpile dependencies like node-excel-export.

Could you add a main file in the package.json, to point to a transpiled dist file perhaps, done by babel?

I could make a PR for this if you are open to it.

[mykeels]

#33