Correct DOCTYPE of GWT widgetset

documentation/clientside/clientside-module.asciidoc

@@ -20,8 +20,8 @@ widget set, you should normally inherit the [classname]#DefaultWidgetSet#.
 
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE module PUBLIC
-  "-//Google Inc.//DTD Google Web Toolkit 1.7.0//EN"
-  "http://google-web-toolkit.googlecode.com/svn/tags/1.7.0/distro-source/core/src/gwt-module.dtd">
+  "-//Google Inc.//DTD Google Web Toolkit 2.8.1//EN"
+  "http://gwtproject.org/doctype/2.8.1/gwt-module.dtd">
 
 <module>
     <!-- Inherit the default widget set -->