bug fix for disconnected springs - all the physics solvers check for connected so only include those

lib/network/modules/PhysicsEngine.js

@@ -498,7 +498,7 @@ class PhysicsEngine {
       for (let edgeId in edges) {
         if (edges.hasOwnProperty(edgeId)) {
           let edge = edges[edgeId];
-          if (edge.options.physics === true) {
+          if (edge.options.physics === true && edge.connected === true) {
             physicsWorkerEdges[edgeId] = {
               connected: edge.connected,
               id: edge.id,