Clear pathElems on clear of canvas

Missed that !29 (merged) had not moved that fix (the bug had existed already earlier) to the new canvas.js file (fixes #41 (closed))

@mnr17 Please review

src/canvas.js

@@ -88,6 +88,7 @@ export const renderPath = (id, points) => {
 }
 
 export const clear = () => {
+  pathElems.clear()
   canvas.innerHTML = ""
 }