fix ChangeType type in TS definition

[Yuri Guller]

The ChangeType is now exported as enum, which is erased in runtime and since the OO self doesn't export such a thing, it just fails in the compiled TS' output.
The best way to handle this, as I understand now, is:

export type ChangeType = 'insert' | 'update' | 'delete' | 'reverse' | 'shuffle';