Fix the numpy12 env

Author: jdavies-st

tox.ini

@@ -18,7 +18,7 @@ deps=
     legacy: numpy~=1.10.0
     numpy11,numpy12,legacy: astropy~=3.0.0
     numpy11: numpy==1.11
-    numpy12: numpy==1.12
+    numpy12: numpy==1.12, gwcs==0.9.1
     numpydev,astrodev,s390x: cython
 extras= all,tests
 # astropy will complain if the home directory is missing