ES6 Purely Functional Solution For Exercise #16

[RavenHursT]

The solution here contains some mutable variables and a for loop (.forEach()): https://github.com/timoxley/functional-javascript-workshop/blob/master/exercises/recursion/solution/solution.js

Just thought I'd submit my functional solution that came out a bit closer to a purely functional one:
https://repl.it/@RavenHursT/Functional-JS-Workshop-Exercise-16-Solution