Update tox.ini

tox.ini

@@ -6,19 +6,16 @@ envlist =
     build_docs
     linkcheck
     codestyle
-requires =
-    setuptools >= 30.3.0
-    pip >= 19.3.1
-isolated_build = true
-indexserver =
-    NIGHTLY = https://pypi.anaconda.org/scientific-python-nightly-wheels/simple
 
 [testenv]
+
 # Suppress display of matplotlib plots generated during docs build
-setenv = MPLBACKEND=agg
+setenv =
+    MPLBACKEND=agg
+    devdeps: PIP_EXTRA_INDEX_URL = https://pypi.anaconda.org/astropy/simple https://pypi.anaconda.org/scientific-python-nightly-wheels/simple
 
 # Pass through the following environment variables which may be needed for the CI
-passenv = HOME, WINDIR, LC_ALL, LC_CTYPE, CC, CI, TRAVIS
+passenv = HOME,WINDIR,LC_ALL,LC_CTYPE,CC,CI
 
 # Run the tests in a temporary directory to make sure that we don't import
 # this package from the source tree
@@ -63,7 +60,7 @@ deps =
     astropy42: astropy==4.2.*
 
     devdeps: numpy>=0.0.dev0
-    devdeps: git+https://github.com/astropy/astropy.git#egg=astropy
+    devdeps: astropy>=0.0.dev0
 
 # The following indicates which extras_require from setup.cfg will be installed
 extras =