title: doctrine:migrations:diff give "No changes detected in your mapping information"
body: <p>I'm using doctrine in combination with symfony. For the database setup I'm using annotations. I created a table successfully but gave the wrong format <code>integer</code> for a field <code>city</code> which I need to change to <code>string</code>. My understanding was, that when I'm changing the annotations in the customers class from </p>
  
  <pre><code>class Customer{
  
    /**
     * @ORM\Column(type="integer", nullable=true)
     * @var string city
     */
    private $city;
  
  }
  </code></pre>
  
  <p>to </p>
  
  <pre><code>class Customer{
  
    /**
     * @ORM\Column(nullable=true)
     * @var string city
     */
    private $city;
  
  }
  </code></pre>
  
  <p>and then run</p>
  
  <pre><code>php bin/console doctrine:migrations:diff
  </code></pre>
  
  <p>all changes of the mapping should be recognized and a php file should be generated containing an ALTER TABLE query or similar. However, this command replies with a <strong>"No changes detected in your mapping information"</strong>. What am I missing?</p>