[Spring Server] Syntax error with Excel MIME Type

Description

The generated API comes witH syntax error when I use application/vnd.ms-excel to describe a response. Note the produces parameter, it contains two entries and no comma:

@RequestMapping(value = "/oper-units/{operUnitId}/data-import-model",
        produces = { "application/vnd.ms-excel""application/json" }, 
        method = RequestMethod.GET)
    ResponseEntity<?> getDataImportModel(@ApiParam(value = "ID da unidade",required=true) @PathVariable("operUnitId") Integer operUnitId);

Swagger-codegen version

swagger-codegen-cli-3.0.0-SNAPSHOT

Swagger declaration file content or url

openapi: "3.0.0"
(...)
      responses:
        '200':
          description: successful operation
          content:
            application/vnd.ms-excel:
              schema:
                type: string

Command line used for generation

java -jar swagger-codegen.jar generate -i ../../openapi.yaml -l spring -o ../..

Steps to reproduce

Related issues/PRs

Suggest a fix/enhancement

Reproduce the issue with the supplied OpenAPI declaration and the swagger-codegen-cli-3.0.0-SNAPSHOT Spring generation command. Inspect the Spring server generation entry point for how multiple response MIME types are rendered, then verify that the generated produces annotation separates application/vnd.ms-excel and application/json correctly and produces valid Java.