title: Monolog not logging context
body: <p>In my Symfony 3.4. application I have configured a custom logger:</p>
  
  <pre><code>monolog:
    handlers:
      my_channel:
        level: debug
        type: stream
        path: '%kernel.logs_dir%/my_channel.log'
        max_files: 10
        channels: [my_channel]
  </code></pre>
  
  <p>When I use this logger in my Code which I have injected correctly with the channel "my_channel".</p>
  
  <pre><code> $this-&gt;logger-&gt;error('error message', $data = ['my context here']);
  </code></pre>
  
  <p>On the screen I get $data info correctly shown:</p>
  
  <pre><code>09:00:08 ERROR     [my_channel] error message ["my context here"]
  </code></pre>
  
  <p>but not in my logs the context is empty:</p>
  
  <pre><code>09:00:08 ERROR     [my_channel] error message []
  </code></pre>
  
  <p><strong>Question</strong>: How can I log the context to my log files too?</p>