Update WpProQuiz_Helper_DbUpgrade.php

MySQL Error:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' `matrix_sort_answer_criteria_width` int(10) unsigned NOT NULL, PRIM' at line 17
Merge pull request #1 from xeno010/patch-1

Fix extra comma in SQL create table statement, WpProQuiz_Helper_DbUpgrade.php

Thanks, xeno010!