uuid format

[alexandruluca]

Hi. Could you also add uuid format support?
Example:

joi
  .string()
  .guid({
    version: [
      'uuidv1'
    ]
  })
  .required();

let eventSchema = {
  startTime: eventStartTimeSchema
};

should convert to

{ type: 'object',
  properties: { startTime: { type: 'string', format: 'uuid' } },
  additionalProperties: false,
  patterns: [],
  required: [ 'startTime' ] }

[alexandruluca]

PS: Is this still maintained? I'd be happy to create a PR if it would be merged