fix: install the latest version of R on ubuntu

Author: eitsupi

src/r-apt/install.sh

@@ -135,6 +135,9 @@ check_packages curl ca-certificates
 # shellcheck source=/dev/null
 source /etc/os-release
 if [ "${ID}" = "ubuntu" ]; then
+    echo "Set up for Ubuntu..."
+    curl -fsSL https://cloud.r-project.org/bin/linux/ubuntu/marutter_pubkey.asc | tee -a /etc/apt/trusted.gpg.d/cran_ubuntu_key.asc >/dev/null
+    echo "deb https://cloud.r-project.org/bin/linux/ubuntu ${UBUNTU_CODENAME}-cran40/" >/etc/apt/sources.list.d/cran-ubuntu.list
     echo "Set up r2u..."
     curl -fsSL https://eddelbuettel.github.io/r2u/assets/dirk_eddelbuettel_key.asc | tee -a /etc/apt/trusted.gpg.d/cranapt_key.asc >/dev/null
     echo "deb https://r2u.stat.illinois.edu/ubuntu ${UBUNTU_CODENAME} main" >/etc/apt/sources.list.d/cranapt.list