That didn't solve it for me but this did (just in case this works for someone else)
sudo add-apt-repository -y "ppa:marutter/rrutter"
sudo add-apt-repository -y "ppa:marutter/c2d4u"
sudo apt-get update
sudo apt-get install r-cran-rstan
sudo apt-get install r-cran-shinystan
sudo apt-get install r-cran-brms