Fix the cell content written for bool type

examples/hello/main.cpp

@@ -13,6 +13,9 @@ int main()
     QXlsx::Workbook workbook;
     QXlsx::Worksheet *sheet = workbook.addWorksheet();
     sheet->write("A1", "Hello Qt!");
+    sheet->write("B3", 12345);
+    sheet->write("C5", "=44+33");
+    sheet->write("D7", true);
     workbook.save(DATA_PATH"Test.xlsx");
     workbook.save(DATA_PATH"Test.zip");
     return 0;

src/xlsxworksheet.cpp

@@ -413,7 +413,7 @@ void Worksheet::writeCellData(XmlStreamWriter &writer, int row, int col, const X
 
     } else if (data.dataType == XlsxCellData::Boolean) {
         writer.writeAttribute("t", "b");
-        writer.writeTextElement("v", data.value.toBool() ? "True" : "False");
+        writer.writeTextElement("v", data.value.toBool() ? "1" : "0");
     } else if (data.dataType == XlsxCellData::Blank) {
         //Ok, empty here.
     }