Fix Checkstyle suppressions DTD link.
diff --git a/checkstyle-suppressions.xml b/checkstyle-suppressions.xml
index 4058b5b..fff8bd5 100755
--- 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">
 <!--
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    contributor license agreements.  See the NOTICE file distributed with