Update checkstyle dtd

checkstyle.xml

 <?xml version="1.0"?>
-<!DOCTYPE module PUBLIC "-//Puppy Crawl//DTD Check Configuration 1.2//EN"
-                        "http://www.puppycrawl.com/dtds/configuration_1_2.dtd">
+<!DOCTYPE module PUBLIC
+   "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+   "https://checkstyle.org/dtds/configuration_1_3.dtd">
 
 <module name="Checker">
     <module name="TreeWalker">