function merge (a, b, options) {
  options = options || {}
  var _with = null
  if (options.array === 'replace') {
    _with = _replaceArrays
  } else if (options.array === 'concat') {
    _with = _concatArrays
  }
  if (_with) {
    return _mergeWith(a, b, _with)
  } else {
    return _merge(a, b)
  }
}
Same as lodash/merge except that it provides options how to
  treat arrays.

  The default implementation overwrites elements.
   get concatenated rather than overwritten.