Use dist: focal on Travis

Fixes

  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.

during pip install cryptography in python: pypy builds.

NB: dist: bionic/focal do not have python: pypy but do have pypy2.

.travis.yml

@@ -1,12 +1,13 @@
 language: python
+dist: focal
 cache: pip
 python:
   - 2.7
   - 3.6
   - 3.7
   - 3.8
   - 3.9
-  - pypy
+  - pypy2
   - pypy3
 install:
   - pip install pytest coverage coverage-python-version coveralls flake8