[tox] apicheck,configcheck: warnings are not errors

tox.ini

@@ -28,12 +28,12 @@ basepython =
 [testenv:apicheck]
 commands =
     pip install -U -r{toxinidir}/requirements/dev.txt
-    sphinx-build -W -b apicheck -d {envtmpdir}/doctrees docs docs/_build/apicheck
+    sphinx-build -b apicheck -d {envtmpdir}/doctrees docs docs/_build/apicheck
 
 [testenv:configcheck]
 commands =
     pip install -U -r{toxinidir}/requirements/dev.txt
-    sphinx-build -W -b configcheck -d {envtmpdir}/doctrees docs docs/_build/configcheck
+    sphinx-build -b configcheck -d {envtmpdir}/doctrees docs docs/_build/configcheck
 
 [testenv:linkcheck]
 commands =