docs: function messageFormat (type, inspect) {
    var msg = this.detailed
      ? 'expect %s `%s`, but %s `%s` given'
      : 'expect `%s`, but `%s` given'
    return this.detailed
      ? util.format(msg, type.expected, inspect.expected, type.actual, inspect.actual)
      : util.format(msg, type.expected, type.actual)
  }