title: fabric.js updating Line coordinates inside of a Group
body: <p>I have set up the functionality that I want with a regular line using fabric.js.  See the code pen below. I can hit the add arrow button to add a line to the canvas and then double click on the line to see 2 circles show up that I can then drag around to move either end of the line.</p>
  <p><a href="https://codepen.io/jrabes/pen/KKZEBVe" rel="nofollow noreferrer">https://codepen.io/jrabes/pen/KKZEBVe</a></p>
  <p>I want to make this line an arrow with the same functionality.  When I add the line and a triangle for the arrow head to a <code>fabric.Group</code> and then try to update the coordinates for the line, the line gets thrown out of the group and I can't select it anymore.  I set up a code pen with what I've been trying below.</p>
  <p><a href="https://codepen.io/jrabes/pen/VwyRBVp" rel="nofollow noreferrer">https://codepen.io/jrabes/pen/VwyRBVp</a></p>
  <p>After double clicking on the line in the group and moving the left circle:
  <img src="https://i.stack.imgur.com/kLJpA.png" alt="after double clicking on the line in the group and moving the left circle" /><br />
  Group selected and still showing original line location after editing line:<br />
  <img src="https://i.stack.imgur.com/lojlV.png" alt="group selected and still showing original line location after editing line" /></p>
  <p>I'm not attached to this particular set up at all, so if there is a different/easier way to get an arrow set up with the ability to edit the endpoints I would love that.</p>