Polish "Use Java 8 LocalDate instead of java.util.Date"

Closes gh-328

src/main/java/org/springframework/samples/petclinic/owner/Pet.java

 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2018 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.

src/main/java/org/springframework/samples/petclinic/visit/Visit.java

 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2018 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.

src/test/java/org/springframework/samples/petclinic/service/ClinicServiceTests.java

+/*
+ * 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License 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.
+ */
+
 package org.springframework.samples.petclinic.service;
 
 import static org.assertj.core.api.Assertions.assertThat;