Remove event listener `touchstart` after adding it. (#205)
Remove event listener `touchstart` after adding it. (#205)

* Remove event listener `touchstart` after adding it.

Issue: when you start drawing by mouse and change to drawing by touch , the mouse button stay triggered. causing the undesired drawing on the canvas.
Fix: Remove event listener `touchstart` after adding it.
Explanation: After changing from `this.ontouchstart` to `this.addEventListener('touchstart')`. we should replace `this.ontouchstart = null;` by `this.removeEventListener('touchstart', startTouchDrawing)`
thomasjbradley/signature-pad