Revert astropy dev command

Author: pllim

tox.ini

@@ -15,7 +15,7 @@ extras = test
 changedir =
   test: .tmp/{envname}
 deps =
-  devdeps: pip install -U -i https://pypi.anaconda.org/astropy/simple astropy --pre
+  devdeps: git+https://github.com/astropy/astropy.git#egg=astropy
   devdeps: git+https://github.com/ejeschke/ginga.git#egg=ginga
 commands =
   jupyter --paths