Fix problems in SpringBootMockUtil reported by Checkstyle

spring-boot-test/src/main/java/org/springframework/boot/test/mock/mockito/SpringBootMockUtil.java

@@ -36,7 +36,7 @@ import org.springframework.util.ReflectionUtils;
  *
  * @author Andy Wilkinson
  */
-class SpringBootMockUtil {
+final class SpringBootMockUtil {
 
 	private static final MockUtilAdapter adapter;
 
@@ -50,6 +50,10 @@ class SpringBootMockUtil {
 		}
 	}
 
+	private SpringBootMockUtil() {
+
+	}
+
 	static MockCreationSettings<?> getMockSettings(Object mock) {
 		return adapter.getMockSettings(mock);
 	}