Fix backgroundColor option documentation (Fix #1164)

src/Renderer.js

@@ -353,8 +353,8 @@ export default class Renderer {
     render(stack: StackingContext): Promise<*> {
         if (this.options.backgroundColor) {
             this.target.rectangle(
-                0,
-                0,
+                this.options.x,
+                this.options.y,
                 this.options.width,
                 this.options.height,
                 this.options.backgroundColor

src/index.js

@@ -64,6 +64,7 @@ const html2canvas = (element: HTMLElement, conf: ?Options): Promise<*> => {
     const defaultOptions = {
         async: true,
         allowTaint: false,
+        backgroundColor: '#ffffff',
         imageTimeout: 15000,
         logging: true,
         proxy: null,