Travis pypy build fails because of stale openssl

[moskupols]

This build of a branch that doesn't do anything with ssl/paramiko fails just for pypy: https://travis-ci.org/github/tomerfiliba/plumbum/builds/747879936 As far as I understand, the reason is that paramiko depends on cryptography, and release of cryptography==3.2.0 dropped support for OpenSSL 1.0.0: https://cryptography.io/en/latest/changelog.html#v3-2 At the time of the last commit to the master that version of cryptography was not released yet, so that's why the problem did not affect the status of master (yet).

I'm not sure why the only failing build is the pypy one, but it fails consistently while the other python builds don't. Maybe travis has slightly different VM images for different python implementations?

I see a couple of possible solutions on .travis.yml side:

• Add something like sudo apt install libssl1.1 to travis.sh
• Add something like env: CRYPTOGRAPHY_ALLOW_OPENSSL_102=1 to pypy configuration

Unfortunately I don't have a set up to test these options, but it should suffice.

[moskupols]

Oh, I guess I can just test these approaches with a new PR.