update license header

Author: kroepke

src/main/java/org/graylog/plugins/usagestatistics/dto/AlarmStats.java

@@ -1,3 +1,18 @@
+/**
+ * Copyright (C) 2015 Graylog, Inc. ([email protected])
+ *
+ * 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.graylog.plugins.usagestatistics.dto;
 
 import com.fasterxml.jackson.annotation.JsonAutoDetect;