Change touchstart to touchend

[arthurmchr]

Since iOS 9, Web audio sounds have to be played at touchend, touchstart will not any more start them.

[mattdesl]

Good call! Does the tap-event module work like this, though?

Another annoying thing with this iOS bug is that you ned to discard anything that the browser might recognize as a "drag" instead of a tap. e.g. too much movement or having the finger held down too long.