The version of icecast available in the 14.04 default repositories isn’t the most up to date. Rather than downloading the .deb package you can simply add their repository to your installation:
sudo sh -c "echo deb http://download.opensuse.org/repositories/multimedia:/xiph/xUbuntu_14.04/ ./ >>/etc/apt/sources.list.d/icecast.list" wget -qO - http://icecast.org/multimedia-obs.key | sudo apt-key add -
Sources: