run correct answer feedback through MathJax filter

Author: PhilippImhof

renderer.php

@@ -854,7 +854,7 @@ public function part_correct_response($part) {
         return html_writer::nonempty_tag(
             'div',
             get_string($string, 'qtype_formulas', $answertext),
-            ['class' => 'formulaspartcorrectanswer'],
+            ['class' => 'formulaspartcorrectanswer filter_mathjaxloader_equation'],
         );
     }