Fix typo in error message.

js/rhino/src/org/mozilla/javascript/resources/Messages.properties

@@ -508,7 +508,7 @@ msg.assn.create.strict =\
     Assignment to undeclared variable {0}
 
 msg.ref.undefined.prop =\
-    Referenced to undefined property "{0}"
+    Reference to undefined property "{0}"
 
 msg.prop.not.found =\
     Property {0} not found.