fix mouse coords when zoomed

src/main.js

@@ -921,8 +921,8 @@ function vectorDist(a, b) {
 function getMousePos(canvas, evt) {
   var rect = canvas.getBoundingClientRect();
   return {
-    x: evt.clientX - rect.left,
-    y: evt.clientY - rect.top
+    x: (evt.clientX - rect.left) / zoomLevel,
+    y: (evt.clientY - rect.top) / zoomLevel
   };
 }