Update popit-api to latest version
Update popit-api to latest version

This includes the fix for deleting memberships when an object is
deleted.

mysociety/popit,Sinar/popit,Sinar/popit,mysociety/popit,Sinar/popit,mysociety/popit,mysociety/popit,openstate/popit,openstate/popit,Sinar/popit,openstate/popit,mysociety/popit,openstate/popit