Fix checkstyle violations in samples

spring-boot-samples/spring-boot-sample-cache/src/main/java/sample/cache/SampleClient.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -53,7 +53,7 @@ class SampleClient {
 
 	private final Random random;
 
-	public SampleClient(CountryRepository countryService) {
+	SampleClient(CountryRepository countryService) {
 		this.countryService = countryService;
 		this.random = new Random();
 	}