title: Postgres 9.4 Add INDEX USING GIN
body: <p>I am using Postgres 9.4, JSONB fields, those are working good.
  But when I add GIN index doctrine migration fails to created index.</p>
  
  <pre><code>class Version20160314132147_Gin_Indexes_content   extends AbstractMigration {
  
  public function up(Schema $schema) {
      $this-&gt;addSql('CREATE INDEX contents_properties_ix ON contents USING gin (properties);');
  }
  
  /**
   * @param Schema $schema
   */
  public function down(Schema $schema) {
      $this-&gt;addSql('DROP INDEX contents_properties_ix;');
  }
  }
  </code></pre>
  
  <p>Error:
  [Doctrine\DBAL\Driver\PDOException]
    SQLSTATE[42704]: Undefined object: 7 ERROR:  data type json has no default operator class for access method "gin"
    HINT:  You must specify an operator class for the index or define a default operator class for the data type.</p>
  
  <p>Composer.json
      {
          "slim/slim": "~2.6",
          "doctrine/orm": "~2.5",
          "doctrine/dbal": "2.5",
          "symfony/yaml": "2.8.<em>@dev",
          "doctrine/cache": "~1.5@dev",
          "symfony/console": "2.8.</em>@dev",
          "symfony/class-loader": "^2.7.4",
          "doctrine/migrations": "~1.0",
          "predis/predis": "~1.0.1",
          "guzzlehttp/guzzle": "~5.0",
          "twig/twig": "~1.0",
          "php-di/php-di": "^5.1.0",
          "monolog/monolog": "~1.15@dev",
          "boldtrn/jsonb-bundle": "~1.0",
          "opsway/doctrine-dbal-postgresql": "~0.1",
          "fzaninotto/faker": "~1.3.0",
          "aws/aws-sdk-php": "^3.9"
      }</p>