title: FabricJS - Avoid triggering "canvas.on('mouse:up', function() { ... })" after object end moving
body: <p>Using FabricJS I'm making a canvas with the possibility to add rectangle.
  Once a rectangle is added to canvas, it can be dragged in any position.</p>
  
  <p>My problem is that when I stop dragging a rectangle, the event:</p>
  
  <pre><code>canvas.on('mouse:up', function(element) { ... });
  </code></pre>
  
  <p>is triggered, but this is an unwanted behavior.</p>
  
  <p>How can I trigger the event:</p>
  
  <pre><code>canvas.on('mouse:up', function(element) { ... });
  </code></pre>
  
  <p>only when is effectively clicked the left button mouse, and not also when I end dragging object?</p>