BUGFIX: Incorrect function call for markAsVoted

Some left over legacy code slipped through when merging. `Poll::markasVoted()` should be called through the `voteHandler` instead of relying on hard coded cookie storing functionality.

code/Poll.php

@@ -136,7 +136,7 @@ function getMaxVotes() {
 	 * Mark the the poll has been voted by the user, which determined by browser cookie
 	 */
 	function markAsVoted() {
-		Cookie::set(self::COOKIE_PREFIX . $this->ID, 1);
+		return $this->voteHandler->markAsVoted();
 	}
 
 	/**