Merge pull request #75 from jhlegarreta/FixNotebooksEnvWarning

MAINT: Fix `notebooks` testing configuration `env` warning

Author: oesteban

tox.ini

@@ -62,7 +62,7 @@ pass_env =
   PYTHONHASHSEED
   ITK_GLOBAL_DEFAULT_NUMBER_OF_THREADS
   PATH
-extras = notebooks
+extras = test, notebooks
 commands =
    # pytest --nbmake docs/notebooks/*.ipynb
    # not working due to https://github.com/tox-dev/tox/issues/1571