Get R 3.3.x to work on Ubuntu 18.04

[grssnbchr]

When trying to run, R has a problem because of libcurl. Obviously, v4 is installed, but v3 needed:

Error in dyn.load(file, DLLpath = DLLpath, ...) : 
  unable to load shared object '/home/tgrossen/R/x86_64-pc-linux-gnu-library/3.3/curl/libs/curl.so':
  /usr/lib/x86_64-linux-gnu/libcurl.so.4: version `CURL_OPENSSL_3' not found (required by /home/tgrossen/R/x86_64-pc-linux-gnu-library/3.3/curl/libs/curl.so)

This is probably just one of many other issues that will arise when trying to run old R versions on new OSes.

Some context: https://community.rstudio.com/t/error-version-curl-openssl-3-not-found/8090

[grssnbchr]

Reinstalling the curl R package solves the problem.