Change R apt repo to use rstudio official

[nuwang]

The existing repo throws the following error: amazon-ebs: TASK: [galaxyprojectdotorg.cloudman-image | Install new r-base 3.2.2 or above] ** amazon-ebs: failed: [localhost] => {"failed": true} amazon-ebs: stderr: E: Version '3.2' for 'r-base' was not found amazon-ebs: amazon-ebs: stdout: Reading package lists... amazon-ebs: Building dependency tree... amazon-ebs: Reading state information... amazon-ebs: amazon-ebs: msg: '/usr/bin/apt-get -y -o "Dpkg::Options::=--force-confdef" -o "Dpkg::Options::=--force-confold" install 'r-base=3.2'' failed: E: Version '3.2' for 'r-base' was not found