Use appropriate Checkstyle DTD
The former URL returned HTTP 404.
<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
- "-//Puppy Crawl//DTD Check Configuration 1.2//EN"
- "http://www.puppycrawl.com/dtds/configuration_1_2.dtd">
+ "-//Checkstyle//DTD Checkstyle Configuration 1.2//EN"
+ "https://checkstyle.org/dtds/configuration_1_2.dtd">
<module name="Checker">
<!--
