[Checkins] [zopefoundation/transaction] 2cfd30: Use dist: focal on Travis

[Marius Gedminas]

  Branch: refs/heads/modern-openssl-please
  Home:   https://github.com/zopefoundation/transaction
  Commit: 2cfd30163e2cd1888add89b43a8d0678c7cb1439
      https://github.com/zopefoundation/transaction/commit/2cfd30163e2cd1888add89b43a8d0678c7cb1439
  Author: Marius Gedminas <marius at gedmin.as>
  Date:   2020-10-30 (Fri, 30 Oct 2020)

  Changed paths:
    M .travis.yml

  Log Message:
  -----------
  Use dist: focal on Travis

The xenial build of pypy on Travis CI links against OpenSSL 1.0.2, which
causes pip install cryptography to fail with

    RuntimeError: You are linking against OpenSSL 1.0.2, which is no longer
    supported by the OpenSSL project. To use this version of cryptography
    you need to upgrade to a newer version of OpenSSL. For this version only
    you can also set the environment variable CRYPTOGRAPHY_ALLOW_OPENSSL_102
    to allow OpenSSL 1.0.2.

Note that 'pypy' is not a valid Python version when using dist: bionic
or dist: focal and you have to use 'pypy2' instead.