Fix date format (no longer localized though)

Author: aadnk

src/main/java/com/comphenix/rema1000/io/excel/ExcelWriter.java

@@ -83,7 +83,7 @@ private void writeTransactions(WorkbookStyle workbookStyle, Worksheet sheet, Lis
     private WorkbookStyle createWorkbookStyle() {
         return new WorkbookStyle(
             (sheet, r, c) -> sheet.style(r, c).bold().set(),
-            (sheet, r, c) -> sheet.style(r, c).format(Integer.toString(0x16)).set()
+            (sheet, r, c) -> sheet.style(r, c).format("yyyy-mm-dd hh:mm:ss").set()
         );
     }
 }