README: use py3 deps

1 job for py3 in 39 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Quality Assurance
failed linters #6123
allowed to fail

00:00:39

 
Name Stage Failure
failed
linters Quality Assurance
client.py:1023:5: E266 too many leading '#' for block comment
client.py:1024:5: E266 too many leading '#' for block comment
client.py:1025:5: E266 too many leading '#' for block comment
ERROR: InvocationError for command /builds/nounous/cranspasswords/.tox/linters/bin/flake8 client.py (exited with code 1)
___________________________________ summary ____________________________________
ERROR: linters: commands failed
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1