Fixed some missing dependencies in network

lib/network/Edge.js

@@ -1,4 +1,5 @@
 var util = require('../util');
+var Node = require('./Node');
 
 /**
  * @class Edge

lib/network/mixins/ManipulationMixin.js

@@ -1,4 +1,6 @@
 var util = require('../../util');
+var Node = require('../Node');
+var Edge = require('../Edge');
 
 /**
  * clears the toolbar div element of children