Added py25 tox target.
Added py25 tox target.

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