fix unicode symbols

The phpmathpublisher update in 7823a7f
changed which fonts are used to render texts. This broke the display of
some unicode symbols like Ω.

This reverts to the use of the FreeSerif and FreeSerifItalic fonts.

deleted.files

@@ -2,5 +2,4 @@ phpmathpublisher/CHANGELOG
 phpmathpublisher/COPYING
 phpmathpublisher/expression_math.php
 phpmathpublisher/expression_texte.php
-phpmathpublisher/fonts/FreeSerifItalic.ttf
 phpmathpublisher/mathpublisher.php

phpmathpublisher/Helper.php

@@ -743,9 +743,9 @@ public function displayMath($text, $size)
         if (isset($fontsMath[$text])) {
             $font = $dirFonts . "/" . $fontsMath[$text] . ".ttf";
         } elseif (preg_match("#[a-zA-Z]#", $text)) {
-            $font = $dirFonts . "/cmmi10.ttf";
+            $font = $dirFonts . "/FreeSerifItalic.ttf";
         } else {
-            $font = $dirFonts . "/cmr10.ttf";
+            $font = $dirFonts . "/FreeSerif.ttf";
         }
         if (isset($symbols[$text])) {
             $text = $symbols[$text];