Bump nox, virtualenv, pytest-cov versions
async-timeout~=3.0.1
coverage~=5.1
-nox==2019.11.9
+nox==2020.5.24
# Virtualenv 20.0.19 breaks nox randomnly...
-virtualenv==20.0.18
+virtualenv==20.0.21
# Pylint 2.5.0 is broken
pylint==2.5.2
pylint-json2html-v2~=0.2.2
pylint-junit~=0.2.0
pytest~=5.4.2
pytest-asyncio~=0.12.0
-pytest-cov~=2.8.1
+pytest-cov~=2.9.0
pytest-randomly~=3.3.1
pytest-testdox~=1.2.1
pytest-xdist~=1.32.0
