Fix Chrome 0.48 issue

Apparently chrome removed SVGElement.prototype.getTransformToElement,
which is used by dagre-d3 when creating edges. This commit is taken
from a fix in the main repo:
dagrejs@1ef067f

dagrejs#202

lib/create-edge-paths.js

@@ -89,7 +89,9 @@ function createLine(edge, points) {
 
 function getCoords(elem) {
   var bbox = elem.getBBox(),
-      matrix = elem.getTransformToElement(elem.ownerSVGElement)
+      matrix = elem.ownerSVGElement.getScreenCTM()
+        .inverse()
+        .multiply(elem.getScreenCTM())
         .translate(bbox.width / 2, bbox.height / 2);
   return { x: matrix.e, y: matrix.f };
 }