Patch the Perl modules in the frozen TeX Live 2018 snapshot

[riccardoporreca]

Follow-up of https://github.com/rocker-org/rocker-versioned/pull/171#issuecomment-552825592:

• Use the newer version available for the installer in tlnet/tlpkg/TeXLive, to include the fix described in https://github.com/yihui/tinytex/issues/77#issuecomment-466584510.
• As discussed in https://www.preining.info/blog/2019/09/tex-services-at-texlive-info/#comments.
• Optional patch only applied for TeX Live 2018, currently relevant for verse:devel but also ported to verse:latest to be ready for next R release with the update to debian:buster (https://github.com/rocker-org/rocker-versioned/issues/169#issuecomment-549977490).

[riccardoporreca]

rocker/verse:devel built locally as

docker build -t rocker/verse:devel-patch-texlive verse/devel

and tested via

docker run --rm --user=rstudio rocker/verse:devel-patch-texlive R -e \
'cat(file = "~/test.Rmd", "---\ntitle: Untitled\nheader-includes:\n   - \\usepackage{bbm}\noutput: pdf_document\n---\n"); rmarkdown::render("~/test.Rmd")'
## [...]
## Output created: test.pdf

Behavior also confirmed by creating and knitting the R markdown docuent from within RStudio launched via

docker run --rm -p 8787:8787 -e DISABLE_AUTH=true rocker/verse:devel-patch-texlive

[cboettig]

This looks great, thanks for doing the deep dive on this one!