The following steps have been taken:
1. Black was updated to latest version. The code has been formatted with
the new version.
2. The pyupgrade utility is installed. This helped to remove all the
code that was needed to support Python < 3.7.
Fix#541.
Co-authored-by: Inada Naoki <songofacandy@gmail.com>
Adjust the skipif conditional to use the older pytest 2.3 syntax.
(This allows the tests to pass with the system pytest package on RHEL
7.0, since RHEL 7.0 ships pytest 2.3.5.)