I recently heard about UbuntuShowdown apps. There are some very nice apps which I really want to try. I am trying to install these apps by adding repositories as it is mentioned on their page. But at the completion of command, it is showing:

unable to locate package <package name>

For example, after running this command in terminal:

sudo add-apt-repository ppa:brianrobles204/xkcd-browser

sudo apt-get update

sudo apt-get install xkcd-browser

I am getting this at the end

unable to locate package xkcd-browser

Please help.

UbuntuShowDown Apps