set correct default val for gradientUnits

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@193735 13f79535-47bb-0310-9956-ffa450edef68

src/codegen/properties.xml

@@ -1040,7 +1040,7 @@
         <value const="OBJECT_BOUNDING_BOX">objectBoundingBox</value>
       </enumeration>
   </datatype>
-	<default>pad</default> 
+	<default>userSpace</default> 
   </property>
   <property>
     <name>viewBox</name>