Remove: set import, Add: license

Signed-off-by: Fabio José <fabiojose@gmail.com>

api/src/main/java/io/cloudevents/v02/Accessor.java

@@ -1,8 +1,22 @@
+/**
+ * Copyright 2019 The CloudEvents 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 io.cloudevents.v02;
 
 import java.util.Collection;
 import java.util.Objects;
-import java.util.Set;
 
 import io.cloudevents.Attributes;
 import io.cloudevents.CloudEvent;