upgrade - Upgrading to Ringtail 13.04 broke some APT repositories?

When I run sudo apt-get update on Ringtail, I get this:

Err http://overviewer.org debian/./ amd64 Packages
404  NOT FOUND [IP: 208.69.124.224 80]

and

Err http://overviewer.org debian/./ i386 Packages
404  NOT FOUND [IP: 208.69.124.224 80]

I went on the Overviewer channel on Freenode and asked them about the repository, and they checked and say there's nothing wrong with their end, so I uninstalled overviewer on my 12.10-powered laptop, and tried again and it works fine there.

Overviewer IRC snipet:

[08:54]  on our server, i can see the file debian/Packages, but not debian/binary-amd64/Packages
[08:54]  i suspect that something might have changed in ringtail?

Here's the (condensed) contents of my sources.list:

# deb cdrom:[Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5)]/ quantal main restricted
# deb cdrom:[Lubuntu 13.04 _Raring Ringtail_ - Alpha amd64 (20130403)]/ raring main multiverse restricted universe
# deb cdrom:[Ubuntu 13.04 _Raring Ringtail_ - Release amd64 (20130420)]/ raring main restricted
## Added by Seann 27 Dec 2012 - Minecraft Map Overviewer
deb http://overviewer.org/ debian ./

The instructions on Overviewer.org are as follows:

Overviewer.org APT Repository

This is the Overviewer.org APT Repository, which hosts frequent builds of Minecraft Overviewer for use on Debian-based systems, such as Ubuntu or Debian itself. In order to use this repository, add the following line to your /etc/apt/sources.list:

deb http://overviewer.org/debian ./

Then, run apt-get update as root to update your repository information.

Installing Overviewer is as simple as running apt-get install minecraft-overviewer. Since this repository is updated at the same time as the Windows builds on GitHub, you can also upgrade through APT. To upgrade, run apt-get update, then apt-get install minecraft-overviewer again.

And I've done all that, as you can see from my sources.list ... So... what changed between 12.10 and 13.04, and how do I fix it? It's not a REALLY big deal because I was able to download and manually install the update, but it's annoying to say the least.

Your problem is a space in the apt line,

you've got:
deb http://overviewer.org/ debian ./

should be:
deb http://overviewer.org/debian ./