code: function commonSequence(a, b){
      var result = [];
      for (var i = 0; i < Math.min(a.length, b.length); i++){
          if (a[i] === b[i]){
              result.push(a[i]);
          } else {
              break;
          }
      }
      return result;
  }
docs: Returns the initial elements which both input arrays have in common
  @param {Array} - first array to compare
  @param {Array} - second array to compare
  @returns {Array}
  @alias module:common-sequence