index.js
function getLongestArray (arrays) {
  var lengths = arrays.map(array => array.length)
  return Math.max.apply(null, lengths)
}
function getLongestArray (arrays) {
  var lengths = arrays.map(array => array.length)
  return Math.max.apply(null, lengths)
}
Array of arrays in.. Returns the length of the longest one
@returns {number}
@private