bug#48811: R 4.1.0 does not build

[Eric Brown]

meedstrom@teknik.io writes:

> Running ~guix build r-minimal~ fails with the following messages. Sounds like 
> it cannot find the
> style file plain.bst and some math fonts; maybe upstream changed the 
> dependencies. Or I read it
> wrong and it's some other error from the make target "vignettes-no-lattice".
>
> Let me know if it works for you and the issue's on my end.
>

I was able to `guix build r-minimal' and it pulled from the substitute servers.