Add R >= 3.5.0 dependency

[bstaton1]

When working in an R version 3.4.3, I tried to install postpack, but got this error:

Installing package into ‘/gpfs01/home/bas0041/R/x86_64-pc-linux-gnu-library/3.4’
(as ‘lib’ is unspecified)
* installing *source* package ‘postpack’ ...
** R
** data
*** moving datasets to lazyload DB
Warning: file ‘cjs.rda’ has magic number 'RDX3'
  Use of save versions prior to 2 is deprecated
Error in load(zfile, envir = envir) :
  bad restore file magic number (file may be corrupted) -- no data loaded
ERROR: lazydata failed for package ‘postpack’
* removing ‘/gpfs01/home/bas0041/R/x86_64-pc-linux-gnu-library/3.4/postpack’
Error: Failed to install 'postpack' from GitHub:
  (converted from warning) installation of package ‘/tmp/RtmpAkMllW/file79a043b0890c/postpack_0.1.16.tar.gz’ had non-zero exit status

I searched the web and found that this has to do with R versions earlier than 3.5.0.

It has to do with the .rda files that are included in /data/.

The fix is to add a dependency for R to be later than 3.5.0