maxItems (value, schema, opts) {
    if (utils.isArray(value)) {
      return maxLengthCommon('maxItems', value, schema, opts)
    }
  }
Validates the length of the provided array against a maximum value defined by the Schema's `maxItems` keyword.
Validation succeeds if the length of the array is less than, or equal to the value of this keyword.
see http://json-schema.org/latest/json-schema-validation.html#anchor42

@name Schema.validationKeywords.maxItems
@method
@param {*} value Array to be validated.
@param {object} schema Schema containing the `maxItems` keyword.
@param {object} [opts] Configuration options.
@returns {(array|undefined)} Array of errors or `undefined` if valid.