Fix string in header
Fix string in header

Commit ab426a791ad1937ea2cf3b340202b3968a378978 changed
sha1 to sha256.
Need to change string correspondingly

Change-Id: I8b35350c32ab551d513f21325931d6697f62fb2f
Related-Bug: #1759250

openstack/python-neutronclient,openstack/python-neutronclient