fix plus icon for ows server widget in project properties

Author: slarosa

src/ui/qgsprojectpropertiesbase.ui

@@ -1744,7 +1744,7 @@
                       <widget class="QToolButton" name="pbnWMSAddSRS">
                        <property name="icon">
                         <iconset resource="../../images/images.qrc">
-                         <normaloff>:/images/themes/default/mActionSignPlus.png</normaloff>:/images/themes/default/mActionSignPlus.png</iconset>
+                         <normaloff>:/images/themes/default/symbologyAdd.png</normaloff>:/images/themes/default/symbologyAdd.png</iconset>
                        </property>
                       </widget>
                      </item>