[R-sig-Debian] Update on docker Python:3 and adding R:4.x

[Johannes Ranke]

Am Donnerstag, 25. Juni 2020, 05:54:03 CEST schrieb Dirk Eddelbuettel:
> 
>    RUN apt update && apt install -y r-base
> 
> instead.  (I also removed the -t buster-cran40 as the 'highest version
> should win'. That may or may not work. Adjust as needed.)

Removing -t buster-cran40 only installs R 4.0.x if there are no packages left 
on the system that depend on the lower r-api-35. Therefore this should be OK 
for a docker image which does not come with R.

Johannes