[PHP] Wrong arrays of objects code generation

Description

php-symfony for server generates wrong type hinting for setter method when array of object required. This could be found in samples provided by codegen: https://github.com/swagger-api/swagger-codegen/blob/master/samples/server/petstore/php-symfony/SymfonyBundle-php/Model/Pet.php#L230

public function setTags(Tag $tags = null) // << should be an array
{
    $this->tags = $tags;
    return $this;
}

Swagger-codegen version

Both master and 3.0.0.

Swagger declaration file content or url

Pet: 
    id: Pet
    description: "A pet is a person's best friend"
    required: 
      - id
      - name
    properties: 
      id: 
        type: integer
        format: int64
      tags: 
        type: array
        items: 
          $ref: Tag

Tag: 
   id: Tag
   properties: 
     name: 
       type: string
     id: 
       type: integer
       format: int64

Start with samples/server/petstore/php-symfony/SymfonyBundle-php/Model/Pet.php and the Pet/Tag schema shown in the issue. Trace the PHP Symfony generator template that produces setTags; done means the generated setter correctly represents an array of Tag objects, with the sample or relevant generator test regenerated to verify the result.