Upgrade to latest Checkstyle DTDs

See gh-22634

Author: sbrannen

src/checkstyle/checkstyle-suppressions.xml

@@ -1,7 +1,5 @@
 <?xml version="1.0"?>
-<!DOCTYPE suppressions PUBLIC
-    "-//Puppy Crawl//DTD Suppressions 1.1//EN"
-    "http://www.puppycrawl.com/dtds/suppressions_1_1.dtd">
+<!DOCTYPE suppressions PUBLIC "-//Checkstyle//DTD SuppressionFilter Configuration 1.2//EN" "https://checkstyle.org/dtds/suppressions_1_2.dtd">
 <suppressions>
 
 	<!-- global -->

src/checkstyle/checkstyle.xml

@@ -1,7 +1,8 @@
 <?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="com.puppycrawl.tools.checkstyle.Checker">
-	<!-- Supressions -->
+
+	<!-- Suppressions -->
 	<module name="SuppressionFilter">
 		<property name="file" value="${config_loc}/checkstyle-suppressions.xml"/>
 	</module>