add test for a ssl3 problem

[bernt-matthias]

trying to add a test case for a URL that gives me problems (fails also when executing curl http://rest.kegg.jp/conv/ncbi-geneid/dme -L on my ubuntu machine .. so the problem might sit deeper):

curl: (56) OpenSSL SSL_read: error:0A000126:SSL routines::unexpected eof while reading, errno 0

xref https://github.com/conda-forge/r-curl-feedstock/pull/21

not sure if I'm doing this right .. I'm quite new to testthat (but keen on learning by doing) and R is not my primary language.