GWT Error: There is '1' error in 'gwt-module.dtd' - gwt

Question

I am learning GWT and was trying to run this tutorial by Vogella
Using the Eclipse GWT plugin 3.0 on Windows 10 and JDK 11
I get this error on the first line Error: There is '1' error in 'gwt-module.dtd'.
/de.vogella.gwt.helloworld/src/de/vogella/gwt/helloworld/De_vogella_gwt_helloworld.gwt.xml
<?xml version="1.0" encoding="UTF-8"?>
<!--
When updating your version of GWT, you should also update this DTD reference,
so that your app can take advantage of the latest GWT module capabilities.
-->
<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 2.8.1//EN"
"http://gwtproject.org/doctype/2.8.1/gwt-module.dtd">
<module rename-to='de_vogella_gwt_helloworld'>
<!-- Inherit the core Web Toolkit stuff. -->
<inherits name='com.google.gwt.user.User'/>
<!-- Inherit the default GWT style sheet. You can change -->
<!-- the theme of your GWT application by uncommenting -->
<!-- any one of the following lines. -->
<inherits name='com.google.gwt.user.theme.clean.Clean'/>
<!-- <inherits name='com.google.gwt.user.theme.standard.Standard'/> -->
<!-- <inherits name='com.google.gwt.user.theme.chrome.Chrome'/> -->
<!-- <inherits name='com.google.gwt.user.theme.dark.Dark'/> -->
<!-- Other module inherits -->
<!-- Specify the app entry point class. -->
<entry-point class='de.vogella.gwt.helloworld.client.De_vogella_gwt_helloworld'/>
<!-- Specify the paths for translatable code -->
<source path='client'/>
<source path='shared'/>
<!-- allow Super Dev Mode -->
<add-linker name="xsiframe"/>
</module>
I get the same error even from the official GWT tutorial http://www.gwtproject.org/doc/latest/tutorial/index.html

Answer 1

From this post, I found that the dtd generated is wrong.
"http://gwtproject.org/doctype/2.8.1/gwt-module.dtd"
I corrected it to
"http://www.gwtproject.org/doctype/2.8.1/gwt-module.dtd"
and the error went away!