Bump testing dependencies

Author: amorison

tox.ini

@@ -7,8 +7,8 @@ skipsdist=True
 usedevelop=True
 deps =
     pip>=19.3.1
-    pytest>=3.10
-    pytest-cov>=2.6
+    pytest>=6.0
+    pytest-cov>=2.10
 commands =
     stagpy version
     pytest --cov=stagpy --cov-report term-missing {posargs}
@@ -17,15 +17,15 @@ setenv = STAGPY_ISOLATED=True
 [testenv:flake8]
 skip_install = true
 deps =
-    flake8>=3.7
+    flake8>=3.8
     flake8-docstrings>=1.5
 commands =
     flake8 setup.py stagpy/ tests/
 
 
 [pytest]
 testpaths = tests
-python-files = test_*.py
+python_files = test_*.py
 
 [flake8]
 ; E731: do not assign a lambda expresssion