function mostCommonWords(text, n = 1) {
  const words = text.toLowerCase().split(/\W+/);

  const map = words
    .reduce((m, w) => m.set(w, 1 + (m.get(w) || 0)), new Map());

  return Array.from(map.entries())
    .sort((a, b) => b[1] - a[1])
    .slice(0, n)
    .map((w) => w[0]);
}
Given text and banned words,
return the most common words in descending order.
@param {string} text - The text to parse.
@param {number} n - The number of results.
@return {string[]}