added missing license header

poi-util/src/main/java/de/muehlencord/shared/poi/WorkbookApp.java

@@ -1,3 +1,18 @@
+/* 
+ * Copyright 2019 Joern Muehlencord (joern (at) muehlencord.de)
+ *
+ * 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 de.muehlencord.shared.poi;
 
 import de.muehlencord.shared.util.file.FileUtil;
@@ -36,7 +51,7 @@ import org.slf4j.LoggerFactory;
 
 /**
  *
- * @author joern.muehlencord
+ * @author Joern Muehlencord (joern (at) muehlencord.de)
  */
 public class WorkbookApp {