Fix Checkstyle suppressions DTD link.
diff --git a/checkstyle-suppressions.xml b/checkstyle-suppressions.xml
index d1ed70a..2f36a9d 100644
--- a/checkstyle-suppressions.xml
+++ b/checkstyle-suppressions.xml
@@ -1,7 +1,7 @@
<?xml version="1.0"?>
<!DOCTYPE suppressions PUBLIC
"-//Puppy Crawl//DTD Suppressions 1.0//EN"
- "http://www.puppycrawl.com/dtds/suppressions_1_0.dtd">
+ "https://checkstyle.org/dtds/suppressions_1_0.dtd">
<!--
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file distributed with