title: Unknown database type json requested, Doctrine\DBAL\Platforms\MySQL57Platform may not support it
body: <p>In official documentation doctrine say since version 2.6 use json instead json_array. But when i mapping property with type json i get this error </p>
  
  <blockquote>
    <p>Unknown column type "json" requested. Any Doctrine type that you use
    has to be registered with \Doctrine\DBAL\Types\Type::addType()</p>
  </blockquote>
  
  <p>version symfony: </p>
  
  <blockquote>
    <p>Symfony 3.3.2 (kernel: app, env: dev, debug: true)</p>
  </blockquote>
  
  <p>part of require composer.json</p>
  
  <pre><code>"doctrine/doctrine-bundle": "^1.6",
  "doctrine/orm": "^2.5",  
  "symfony/symfony": "3.3.*",
  </code></pre>
  
  <p>official doctrine dbal repository on github has JsonType in folder Types, i have not this. maybe this is my issue ?  then how can i update my doctrine dbal?
  Maybe who knows how resolve problem. </p>
  
  <p>Or maybe just use json_array? can someone advice </p>