Update of versions of the used tools with tox and in the CI build to the latest

This MR is to solve issue #83 (closed)

All the tools have been updated :

CI side:

python:3.8.2
tox==3.14.5
twine==3.1.1

Tox side:

flake8 = 3.7.9
isort = 4.3.21
yapf = 0.29.0
astroid = 2.3.3
pylint = 2.4.4
pytest = 5.4.1
pytest-cov = 2.8.1