Atom XML namespace must be http not https

[swsnr]

Commit 80b2437 changed the Atom xmlns in feed/blog.xml and feed/index.xml to from http://www.w3.org/2005/Atom to https://www.w3.org/2005/Atom`.

This breaks my RSS reader because the namespace is no longer valid; Atom must be http://www.w3.org/2005/Atom, see e.g. https://tools.ietf.org/html/rfc4287#section-1.2

[SethTisue]

Oops! Care to PR the fix?

[swsnr]

Will do 👍

[swsnr]

@SethTisue See #1198