Fix 'canvas is not defined'

Author: GarboMuffin

src/SVGSkin.js

@@ -128,8 +128,9 @@ class SVGSkin extends Skin {
         // regards to memory.
         const textureData = this._context.getImageData(0, 0, this._canvas.width, this._canvas.height);
 
-        canvas.width = 0;
-        canvas.height = 0;
+        // TODO: not sure if this actually does anything meaningful
+        this._canvas.width = 0;
+        this._canvas.height = 0;
 
         const textureOptions = {
             auto: false,