Update tox.ini

Author: C-Achard

tox.ini

@@ -29,6 +29,7 @@ passenv =
 deps =
     pytest  # https://docs.pytest.org/en/latest/contents.html
     pytest-cov  # https://pytest-cov.readthedocs.io/en/latest/
+    dask
 ;    # you can remove these if you don't use them
     napari
     PyQt5