Fixed minor type.
Fixed minor type.

Closes #231.

jkyeung/XlsxWriter,Thhhza/XlsxWriter,mdeemer/XlsxWriter,yaojingwu1992/XlsxWriter,gechong/XlsxWriter,seize-the-dave/XlsxWriter,Thhhza/XlsxWriter,liukaijv/XlsxWriter,mdeemer/XlsxWriter,applicationdevm/XlsxWriter,liukaijv/XlsxWriter,jvrsantacruz/XlsxWriter,liukaijv/XlsxWriter,yaojingwu1992/XlsxWriter,seize-the-dave/XlsxWriter,jvrsantacruz/XlsxWriter,applicationdevm/XlsxWriter,Thhhza/XlsxWriter,Thhhza/XlsxWriter,gechong/XlsxWriter,gechong/XlsxWriter,seize-the-dave/XlsxWriter,jvrsantacruz/XlsxWriter,yaojingwu1992/XlsxWriter,jmcnamara/XlsxWriter,seize-the-dave/XlsxWriter,jkyeung/XlsxWriter,applicationdevm/XlsxWriter,jmcnamara/XlsxWriter,mdeemer/XlsxWriter,jmcnamara/XlsxWriter,jkyeung/XlsxWriter,gechong/XlsxWriter,yaojingwu1992/XlsxWriter,jkyeung/XlsxWriter,mdeemer/XlsxWriter,liukaijv/XlsxWriter,applicationdevm/XlsxWriter,jvrsantacruz/XlsxWriter,jmcnamara/XlsxWriter