For now, the only case this adds is a missing leading zero in the
day of the month of RFC822/RFC1123 - style http dates as in

		Fri, 2 Mar 2018 14:26:02 GMT (bad)
instead of	Fri, 02 Mar 2018 14:26:02 GMT (correct)

This is clearly invalid according to
https://tools.ietf.org/html/rfc7231#section-7.1.1.2
yet accepted by other webserver software.