title: Update graph in cytoscape.js: node positions not updated
body: <p>I have used the following line :</p>
  
  <pre><code> cy.json({ elements: treeData });
  </code></pre>
  
  <p>in order to update the data in my graph (using cytoscape.js). The graph has now the new data but the nodes are in the positions of the previous ones. How can i fix that? I do not have specific positions i want to get the default ones based to the new nodes.</p>