Use releases.openstack.org instead of opendev.org

This is a more stable URL that will redirect to the correct location.

Change-Id: If5ad860a65c1d4934ad47fb06f1f3386b4550008

Author: priteau

tox.ini

@@ -98,7 +98,7 @@ import_exceptions = cloudkittyclient.i18n
 
 [testenv:releasenotes]
 deps =
-  -c{env:TOX_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt
 commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html