Update checkstyle rules to accept variable copyright year (#231)

Author: raphkim

configuration/checkstyle-rules.xml

@@ -24,7 +24,7 @@
     <property name="fileExtensions" value="java" />
 
     <!-- Check that source files have a license header. -->
-    <module name="Header">
+    <module name="RegexpHeader">
         <property name="headerFile" value="configuration/java.header" />
     </module>
 

configuration/java.header

@@ -1,15 +1,15 @@
-/*
- * Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License").
- * You may not use this file except in compliance with the License.
- * A copy of the License is located at
- *
- *  http://aws.amazon.com/apache2.0
- *
- * or in the "license" file accompanying this file. This file is distributed
- * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
- * express or implied. See the License for the specific language governing
- * permissions and limitations under the License.
- */
+^/\*$
+^ \* Copyright \d{4} Amazon\.com, Inc\. or its affiliates\. All Rights Reserved\.$
+^ \*$
+^ \* Licensed under the Apache License, Version 2\.0 \(the \"License\"\)\.$
+^ \* You may not use this file except in compliance with the License\.$
+^ \* A copy of the License is located at$
+^ \*$
+^ \*  http://aws\.amazon\.com/apache2\.0$
+^ \*$
+^ \* or in the \"license\" file accompanying this file\. This file is distributed$
+^ \* on an \"AS IS\" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either$
+^ \* express or implied\. See the License for the specific language governing$
+^ \* permissions and limitations under the License\.$
+^ \*/$