test_cli.py uses removed `md5` module

[rekado]

Describe the bug

The file test_cli.py uses the module md5, which has been removed from Python 3.

To Reproduce Run the test suite with pytest.

Expected behavior Tests pass.

Additional context

The fix is simple:

• replace import md5 with from hashlib import md5
• replace md5.new with md5
• replace digest with hexdigest

[caleblareau]

Thanks-- fortunately only in the test code rather than the main package. I've updated this script in the latest commit.