Fixed xsd in release version (#147)

Co-authored-by: Adam Bem <adam.bem@zoho.eu>
Reviewed-on: #147
Reviewed-by: Dariusz Augustyniak <augustyd@noreply.example.com>

Frontend/tools/xsd.html

@@ -23,6 +23,12 @@
                             <option value="xalan">Xalan</option>
                             <option value="libxml">libXML</option>
                         </select>
+                        <select name="versions" id="versions" style="display: none;">
+                            <option class="hideable libxml xalan"value="1.0">1.0</option>
+                            <option class="hideable saxon" value="2.0">2.0</option>
+                            <option class="hideable saxon" value="3.0">3.0</option>
+                            <option class="hideable saxon" value="3.1">3.1</option>
+                        </select>
                     </div>
                     <div>
                         <button class="action-button active" id="clearXMLButton" style="padding: 3px 10px;"