Instance update does not preserve previous dataValues

instance update calls save() a the end, then in instance.js:

        .then(function(result) {
          options.fields.forEach(function (field) {
            result._previousDataValues[field] = result.dataValues[field];
            self.changed(field, false);
          });
          self.isNewRecord = false;
          return result;
        })

result._previousDataValues is overwritten with new values

[pablodgonzalez]

What About afterUpdate hook? There is a good point to do somethings related to new and old values.

[janmeier]

PRs are always welcome 😃