Merge pull request #2388 from bsipocz/test_add_oldpyvo

TST: Make sure we test with the minimum pyvo requirement

Author: bsipocz

tox.ini

@@ -36,6 +36,7 @@ deps =
     oldestdeps: astropy==4.0
     oldestdeps: numpy==1.16
     oldestdeps: matplotlib==3.3.*
+    oldestdeps: pyvo==1.1
     cov: codecov
 
 extras =