sudo add-apt-repository ppa:staticfloat/juliareleases)and not the nightlies ppa (
sudo apt-add-repository ppa:staticfloat/julianightlies). Try
sudo apt-add-repository --remove ppa:staticfloat/julianightlies
sudo apt-add-repository ppa:staticfloat/juliareleases
sudo apt-get update
sudo apt-get install --reinstall julia
(not positive on the last command, but it's worth a try).
See http://askubuntu.com/questions/307/how-can-ppas-be-removed for removing repos.