* Add assumptions that must be held in assets module * Update srml/assets/src/lib.rs Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com> * Update srml/assets/src/lib.rs Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>