Rework pytest calls and silence datetime warning

tox.ini

@@ -1,5 +1,4 @@
 [tox]
-install_command = pip install {opts} {packages}
 envlist = {py36,py38,py39}-{1.11,2.2,3.2,4.2}, flake8
 
 [testenv]
@@ -9,15 +8,8 @@ setenv =
   TOXENV={envname}
   XUNIT_FILE=pytest-{envname}.xml
 commands =
-    {envbindir}/pytest \
-        --cov=capone\
-        --cov-append \
-        --cov-report xml:coverage/coverage.xml \
-        --cov-report html:coverage/ \
-        --cov-fail-under 100 \
-        --junitxml=$XUNIT_FILE \
-        -v -rx \
-        capone
+  pytest --cov=capone --cov-fail-under 100 {posargs}
+
 deps =
   -r{toxinidir}/requirements-dev.txt
   1.11: Django>=1.11,<2
@@ -62,7 +54,7 @@ deps =
   psycopg2>=2.6.2,<2.9
 
 [testenv:flake8]
-commands = {envbindir}/flake8 -v capone
+commands = flake8 -v capone
 
 [pytest]
 DJANGO_SETTINGS_MODULE = capone.tests.settings