Fix UUID support

[ackintosh]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.4.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

This PR fixes #1733

---

Sample spec

Sample spec

openapi: 3.0.0
info:
  description: >-
    This spec is mainly for testing Petstore server and contains fake endpoints,
    models. Please do not use this for any other purpose. Special characters: "
    \
  version: 1.0.0
  title: OpenAPI Petstore
  license:
    name: Apache-2.0
    url: 'http://www.apache.org/licenses/LICENSE-2.0.html'
paths:
  /foo:
    get:
      parameters:
        - $ref: '#/components/parameters/TestQuery'
      responses:
        default:
          description: response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Foo'
servers:
  - url: http://localhost:8080/
    description: The local server
components:
  parameters:
    TestQuery:
        name: testQuery
        description: test query
        in: query
        schema:
          $ref: '#/components/schemas/Bar'
  schemas:
    Foo:
      type: object
      properties:
        bar:
          $ref: '#/components/schemas/Bar'
    Bar:
      type: string
      format: uuid

Sample code using a generated codes from the spec

fun main(args: Array<String>) {
    val api = DefaultApi()
    println(api.fooGet(UUID.randomUUID()))
}

Before

Exception in thread "main" java.lang.IllegalArgumentException: Platform class java.util.UUID annotated [] requires explicit JsonAdapter to be registered
	at com.squareup.moshi.ClassJsonAdapter$1.create(ClassJsonAdapter.java:51)
	at com.squareup.moshi.Moshi.adapter(Moshi.java:100)
	at com.squareup.moshi.KotlinJsonAdapterFactory.create(KotlinJsonAdapter.kt:184)
	at com.squareup.moshi.Moshi.adapter(Moshi.java:100)
	at com.squareup.moshi.Moshi.adapter(Moshi.java:62)
	at org.openapitools.client.apis.DefaultApi.fooGet(DefaultApi.kt:173)
	at org.openapitools.client.MainKt.main(Main.kt:8)

After

Foo(bar=ce5b8513-fd5b-4b25-98e2-c40dc1b3c7c4)

[wing328]

cc @jimschubert (2017/09) @dr4ke616 (2018/08)

[jimschubert]

This looks good. I haven't run any tests on it, but I don't see any issues with implementation.