Update tox.ini

Co-authored-by: P. L. Lim <[email protected]>

Author: lpsinger

tox.ini

@@ -35,7 +35,7 @@ extras =
 commands_pre=
     numpydev: pip install -U --pre -i https://pypi.anaconda.org/scientific-python-nightly-wheels/simple numpy
     devdeps: pip install -U --pre -i https://pypi.anaconda.org/liberfa/simple pyerfa
-    devdeps: pip install -U --pre -i git+https://github.com/lpsinger/astropy@masked-classes-importable
+    devdeps: pip install git+https://github.com/lpsinger/astropy@masked-classes-importable
 
     # Generate `requiremments-min.txt`
     oldestdeps: minimum_dependencies asdf-astropy --filename {envtmpdir}/requirements-min.txt