The last snapshot was 4 months ago (2020-08-19). I also found that I needed newer definitions when I was trying to fix the R arrow package.
This update required a couple of manual changes:
1. Removing a few deleted packages from default.nix
2. Renaming the "assert" package to "r_assert" in generate-r-packages.R because "assert" is a keyword in Nix
70cd2cb336