Fix basic auth realm syntax

A basic auth realm parameter is a quoted-string [RFC2617][]§1.2; a
quoted-string takes double quotes, not single quotes [RFC2616][]§2.2.

[RFC2616]: http://www.ietf.org/rfc/rfc2616.txt
[RFC2617]: http://www.ietf.org/rfc/rfc2617.txt