not (value, schema, opts) {
    if (!validate(value, schema.not, opts)) {
      // TODO: better messaging
      return makeError('succeeded', 'should have failed', opts)
    }
  }
Validates the provided value is not valid with any of the schemas defined in the Schema's `not` keyword.
An instance is valid against this keyword if and only if it is NOT valid against the schemas in this keyword's value.

see http://json-schema.org/latest/json-schema-validation.html#anchor91
@name Schema.validationKeywords.not
@method
@param {*} value to be checked.
@param {object} schema Schema containing the not keyword.
@param {object} [opts] Configuration options.
@returns {(array|undefined)} Array of errors or `undefined` if valid.