title: Phaser: this.game is undefined in the Update function
body: <p>Good evening,
  sorry for asking again, but I need to be done with this by tomorrow for school. Basically, when I try to access the this.game variable in the update function, it says that it is undefined, to be specific, I get this; "Uncaught TypeError: Cannot read property 'state' of undefined".
  In my update function I have this:</p>
  
  <pre><code>create: function() {
      [...]
      map.setCollisionByExclusion([], true, doorLayer);
      [...]
  }
  </code></pre>
  
  <p>When I try to access this.game in the update function on the collision action, I get the error mentioned above.
  Here's the code;</p>
  
  <pre><code>update: function() {
      [...]
      this.game.physics.arcade.collide(player, doorLayer, function() {
          if (hasItem) {
              this.game.state.start('Hallway'); //This is where I get the error
          }
      });
      [...]
  }
  </code></pre>
  
  <p>Thank you for your time.</p>