Upgrade to Gradle 6.8 and modernize the build

Closes gh-719

docs/src/test/java/com/example/SnippetReuse.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2016 the original author or authors.
+ * Copyright 2014-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@ public class SnippetReuse {
 			linkWithRel("last").optional().description("The last page of results"),
 			linkWithRel("next").optional().description("The next page of results"),
 			linkWithRel("prev").optional().description("The previous page of results"));
+
 	// end::field[]
 
 }