Bar graph added.

node_modules/vega-canvas/index.js

@@ -0,0 +1,13 @@
+import {domCanvas, domImage} from './src/domCanvas';
+import {nodeCanvas, nodeImage} from './src/nodeCanvas';
+
+export {domCanvas} from './src/domCanvas';
+export {nodeCanvas} from './src/nodeCanvas';
+
+export function canvas(w, h, type) {
+  return domCanvas(w, h) || nodeCanvas(w, h, type) || null;
+}
+
+export function image() {
+  return domImage() || nodeImage() || null;
+}