update tox config

tox.ini

@@ -7,29 +7,25 @@ basepython = python3
 
 [testenv]
 recreate = true
-whitelist_externals = poetry
 skip_install = true
+whitelist_externals = poetry
 
 commands =
     poetry install
-    poetry run pytest tests/ --color=yes {posargs} -v
+    poetry run pytest tests/ -v --color=yes {posargs}
 
 [testenv:py37-pytest-coverage]
-recreate = true
-whitelist_externals = poetry
-skip_install = true
 passenv = TRAVIS TRAVIS_*
 
 commands =
     poetry install
-    poetry run pytest tests/ --cov=skmpe --color=yes {posargs} -v
+    poetry run pytest tests/ -v --color=yes --cov=skmpe {posargs}
     coveralls
 
 [testenv:docs]
-whitelist_externals = make
 commands =
-    poetry install
-    make -C docs/ html
+    poetry install --no-dev --extras docs
+    poetry run make -C docs/ html
 
 [testenv:flake8]
 deps =