Update +pages.svelte allow downloading current canvas

Adds the 'Download' control to drawingboard.js.

I have not tested this, assuming this is what's being used?
https://github.com/Leimi/drawingboard.js#included-controls

src/routes/+page.svelte

@@ -298,7 +298,7 @@
 		await tick();
 		drawingBoard = new window.DrawingBoard.Board('board-container', {
 			size: 10,
-			controls: ['Color', { Size: { type: 'dropdown' } }, { DrawingMode: { filler: false } }],
+			controls: ['Color', { Size: { type: 'dropdown' } }, { DrawingMode: { filler: false } }, 'Download'],
 			webStorage: false,
 			enlargeYourContainer: true
 		});