multipleOf (value, schema, opts) {
    const multipleOf = schema.multipleOf
    if (utils.isNumber(value)) {
      if ((value / multipleOf) % 1 !== 0) {
        return makeError(value, `multipleOf ${multipleOf}`, opts)
      }
    }
  }
Validates the provided number is a multiple of the number defined in the Schema's `multipleOf` keyword.
Validation succeeds if the number can be divided equally into the value of this keyword.
see http://json-schema.org/latest/json-schema-validation.html#anchor14

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