[typescript-fetch] (4.0.X) enums in API generator template missing

Created by: someone1

Description

The model mustache template takes into account enums, the api template does not and incorrectly sets the datatype to the enum values.

openapi-generator version

openapi-generator-cli-4.0.0-20181126.024631-44

OpenAPI declaration file content or url

swagger: "2.0"
info:
  title: "Simple Test"

paths:
  "/get/Simple":
    get:
      summary: Retrieve List of Simple
      operationId: "get.Simple"
      parameters:
        - in: query
          name: animal
          type: string
          enum:
            - Cat
            - Dog
            - Tiger
      responses:
        200:
          description: OK

Generated code (excerpt):

export interface GetSimpleRequest {
    animal?: 'Cat' | 'Dog' | 'Tiger';
}

Command line used for generation

openapi-generator generate -i openapi.yaml -l typescript-fetch -c es6.json -o ./typescript-api/

Steps to reproduce

1. Use the provided yaml excerpt above to generate a client with the provided command line
2. Buggy code generated

Related issues/PRs

PR #569

Suggest a fix/enhancement

Update the api mustache template to follow the same enum logic as the model template.