Include joint.graphUtils.js file to your HTML:
<script src="joint.graphUtils.js"></script>If you plan to use shortestPath() method, you're going to also need to include
joint.alg.priorityQueue.js and joint.alg.dijkstra.js plugins:
<script src="joint.alg.priorityQueue.js"></script>
<script src="joint.alg.dijkstra.js"></script>