[SymfonyServerCodegen] Bug: ignore default integer value for models

Description

Default value of integer property in model ignored and used null.
But for string property all ok.

Swagger-codegen version

java -jar swagger-codegen-cli.jar version
2.3.1

Swagger declaration file content or url

https://gist.github.com/4n70w4/fd58b3273461c57e5289e3fb587be71e

      test:
        type: integer
        default: 0
      test2:
        type: string
        default: 0

Command line used for generation

java -jar swagger-codegen-cli.jar generate --input-spec test.yml --lang io.swagger.codegen.languages.SymfonyServerCodegen --output app/demo

Steps to reproduce

see demo/SymfonyBundle-php/Model/ApiResponse.php

    public function __construct(array $data = null)
    {
        $this->test = isset($data['test']) ? $data['test'] : null;
        $this->test2 = isset($data['test2']) ? $data['test2'] : '0';
    }

Why for type: integer; default: 0 generated $data['test'] : null; ?

Related issues/PRs

N/A

Suggest a fix/enhancement

N/A

Reproduce the generation command with the supplied Swagger declaration and inspect demo/SymfonyBundle-php/Model/ApiResponse.php, especially the constructor defaults for test and test2. Trace the SymfonyServerCodegen model template or generator logic that emits these assignments; done means an integer default of 0 is preserved like the string default.