Minor - fix link

Author: jmontoyaa

main/gradebook/index.php

@@ -779,10 +779,8 @@ function confirmation() {
 
 if (!api_is_allowed_to_edit(null, true)) {
     $actionsLeft .= Display::url(
-        Display::returnFontAwesomeIcon('file-pdf-o').get_lang(
-            'DownloadReportPdf'
-        ),
-        api_get_self()."?".api_get_self()."&action=export_table",
+        Display::returnFontAwesomeIcon('file-pdf-o').get_lang('DownloadReportPdf'),
+        api_get_self().'?action=export_table',
         ['class' => 'btn btn-default']
     );
 }