Fix CI

tox.ini

@@ -8,11 +8,16 @@ requires =
 isolated_build = true
 
 [testenv]
+setenv =
+  MPLBACKEND=agg
+  JUPYTER_PLATFORM_DIRS=1
 extras = test
 changedir =
   test: .tmp/{envname}
 deps =
-  devdeps: git+https://github.com/astropy/astropy.git#egg=astropy
+  devdeps: pip install -U -i https://pypi.anaconda.org/astropy/simple astropy --pre
   devdeps: git+https://github.com/ejeschke/ginga.git#egg=ginga
 commands =
+  jupyter --paths
+  pip freeze
   pytest --pyargs astrowidgets {toxinidir}/docs {posargs}