Dredd ^13.0.2 no longer supports byte format

[rohaldb]

Describe the bug
Certain string formats are no longer supported in 13.0.0.
Still working: date, date-time
No longer working: byte, password, binary

To Reproduce
I have a simple express server:

app.get('/', function(req, res) {
  res.json({message: 'Hello World!'});
})

Swagger 2.0 file api-description.yml:

swagger: '2.0'
info:
  version: '1.0'
  title: Example API
  license:
    name: MIT
host: www.example.com
basePath: /
schemes:
  - http
paths:
  /:
    get:
      produces:
        - application/json; charset=utf-8
      responses:
        '200':
          description: ''
          schema:
            type: object
            properties:
              message:
                type: string
                format: byte
            required:
              - message

Running ./node_modules/.bin/dredd with ^13.0.0 fails validation with error
Error: unknown format "byte" is used in schema at path "#/properties/message"

Expected behavior
It should validate successfully, which it does in 12.2.0

What is in your dredd.yml?

color: true
dry-run: null
hookfiles: null
language: nodejs
require: null
server: npm start
server-wait: 3
init: false
custom: {}
names: false
only: []
reporter: apiary
output: []
header: []
sorted: false
user: null
inline-errors: false
details: false
method: []
loglevel: warning
path: []
hooks-worker-timeout: 5000
hooks-worker-connect-timeout: 1500
hooks-worker-connect-retry: 500
hooks-worker-after-connect-wait: 100
hooks-worker-term-timeout: 5000
hooks-worker-term-retry: 500
hooks-worker-handler-host: 127.0.0.1
hooks-worker-handler-port: 61321
config: ./dredd.yml
blueprint: api-description.yml
endpoint: 'http://127.0.0.1:3000'

What's your dredd --version output?
13.0.2

Does dredd --loglevel=debug uncover something?
Nothing I can see

[kylef]

Fwiw, I don't think Dredd ever supported byte format. It's just that in prior versions of Dredd there wasn't any validation in place so Dredd didn't error out when encountering unsupported formats.

I think we can restore this behaviour by passing the unknownFormats option to AJV (the JSON Schema validation library) in Gavel (the validation library Dredd uses), as per Ajv docs:

The option unknownFormats allows changing the default behaviour when an unknown format is encountered. In this case Ajv can either fail schema compilation (default) or ignore it (default in versions before 5.0.0). You also can whitelist specific format(s) to be ignored. See Options for details.

I think this would go into https://github.com/apiaryio/gavel.js/blob/a7d1b5352291c3b360df9df5218d53c86c8b02e2/lib/validators/json-schema-next.js#L174