Update should accept a Partial Model as first parameter

[victorivens05]

The first parameter for update is values: object, where anything can be passed as a parameter, as in the line:

sequelize/lib/model.d.ts

Line 1907 in 69b371d

values: object,

I think it should be values: Partial<M>. That way we could be confident that if we change a parameter in any model, we would see the error, since the value would only accept values present in the model.