common: update models/todo.js signature
common: update models/todo.js signature

Change the function exported by `models/todo.js` to conform to
the new contract expected by loopback-boot: the function exported
has a single argument only.

jeffcressman/loopback-example-offline-sync-react,uniconstructor/loopback-example-offline-sync,jouke/loopback-connector-cordova-sqlite,uniconstructor/loopback-example-offline-sync,jeffcressman/loopback-example-offline-sync-react