I suspect this issue may indeed be temporary, but if you need the heroku toolbelt installed now, you can install the standalone client instead of the ubuntu/debian bundle.
wget -qO- https://toolbelt.heroku.com/install.sh | sh
On an Ubuntu-based distro, however, the above will likely throw some errors:
sh: 7: [[: not found
sh: 29: [[: not found
Installation complete
This is because on Ubuntu systems /bin/sh is dash, not bash. You could either get the script and modify it to use bash instead of sh (sh is called within the script, just changing sh to bash in the command above won't suffice), or, you could ignore the errors and just do what the error-ing portion of the script instructs you to do:
Add the Heroku CLI to your PATH using:
echo 'PATH="/usr/local/heroku/bin:$PATH"' >> ~/.profile
You'll need to logout/login again to register the path addition, or just execute heroku directly in the mean time:
/usr/local/heroku/bin/heroku