Add missing link

Link to rocker-versioned2 repository

bug-fix: libpcre2-8-0 is needed along with libpcre2 for r-devel

Without this library, the following error is produced

```
$$ docker run -it rocker/r-ver:devel bash
root@012af310be7d:/# R
/usr/local/lib/R/bin/exec/R: error while loading shared libraries: libpcre2-8.so.0: cannot open shared object file: No such file or directory
```

The same error doesn't show up in the rocker/rstudio and other
containers which inherit from this image is because another linux package is
installing the dependency libpcre2-8-0 on the succeeding images.

But for the rocker/r-ver:devel image to work, this dependency is needed.

Remove libpcre3 as it causes a conflict while loading libraries

Partial update MRAN dates

Add libpcre2-dev as it is needed by latest r-devel

When the image is r-ver:devel is built without libpcre2-dev,
the following issue is generated.

```
checking whether PCRE support suffices... no
configure: error: PCRE2 library and headers are required, or use --with-pcre1 and PCRE >= 8.32 with UTF-8 support
/bin/sh: 1: Rscript: not found
```

This allows a clean build

Use https to download the .deb file if RSTUDIO_VERSION is provided

3.6.2

Patch error handling of tlmgr path in TeX Live 2016

* See https://tex.stackexchange.com/a/314079.
* Apply the corresponding fix https://git.texlive.info/texlive/commit/Master/tlpkg/TeXLive/TLUtils.pm?id=69cee5e1ce4b20f6ebb6af77e19d49706a842a3e instead of the `||true` workaround from #171.
* Fixes /rocker-org/rocker#370.