Fixed a small positioning issue with dagre demo

The dagre example doesn't take into account that dagre works with center of position for nodes but react-diagrams works with top left of position for nodes.

To correctly position the nodes, half of the width and height should be subtracted from the x and y axis respectively.

demos/demo-dagre/dagre-utils.ts

@@ -11,8 +11,8 @@ export function distributeElements(model) {
 	let nodes = distributeGraph(clonedModel);
 	nodes.forEach(node => {
 		let modelNode = clonedModel.nodes.find(item => item.id === node.id);
-		modelNode.x = node.x;
-		modelNode.y = node.y;
+		modelNode.x = node.x - (node.width / 2);
+		modelNode.y = node.y - (node.height / 2);
 	});
 	return clonedModel;
 }