Method shuffleArray

src/cross-validate.js:46–54

* Randomize array element order in-place. * Using Durstenfeld shuffle algorithm. * source: http://stackoverflow.com/a/12646864/1324039

(array)

   * source: http://stackoverflow.com/a/12646864/1324039
   */
  shuffleArray(array) {
    for (let i = array.length - 1; i > 0; i--) {
      let j = Math.floor(Math.random() * (i + 1));
      let temp = array[i];
      array[i] = array[j];
      array[j] = temp;
    }
    return array;
  }

  /**
   *