Fix Checkstyle configuration DTD link.
diff --git a/checkstyle.xml b/checkstyle.xml
index 8873dd4..6fb154d 100644
--- a/checkstyle.xml
+++ b/checkstyle.xml
@@ -17,8 +17,8 @@
-->
<!DOCTYPE module PUBLIC
- "-//Puppy Crawl//DTD Check Configuration 1.1//EN"
- "http://www.puppycrawl.com/dtds/configuration_1_1.dtd">
+ "-//Checkstyle//DTD Checkstyle Configuration 1.2//EN"
+ "https://checkstyle.org/dtds/configuration_1_2.dtd">
<!-- commons codec customization of default Checkstyle behavior -->
<module name="Checker">