update tox file

tox.ini

@@ -19,11 +19,10 @@ passenv =
 deps =
     pytest  # https://docs.pytest.org/en/latest/contents.html
     pytest-cov  # https://pytest-cov.readthedocs.io/en/latest/
-    pytest-xvfb ; sys_platform == 'linux'
-    # you can remove these if you don't use them
+    pytest-qt  # https://pytest-qt.readthedocs.io/en/latest/
+    coverage
     napari
-    magicgui
-    pytest-qt
-    qtpy
     pyqt5
+    magicgui
+
 commands = pytest -v --color=yes --cov=brainreg_segment --cov-report=xml