Bumping development dependencies versions.

Author: igorborgest

requirements-dev.txt

@@ -7,7 +7,7 @@ mypy~=0.782
 isort~=4.3.21
 pydocstyle~=5.0.2
 doc8~=0.8.1
-tox~=3.15.2
+tox~=3.16.1
 pytest~=5.4.3
 pytest-cov~=2.10.0
 pytest-xdist~=1.32.0