Observer does not work with JSON columns

[miracle2k]

If I observe a JSON column:

base = Column(UnicodeText)
data = Column(JSONB)

@observes('base', 'data')
def translite_observer(self, base, data):
    print(data)

And data is {"a": 1, "b": 2}, and I change the base attribute, then the observer will print:

set('a', 'b')

This is because two is_sequence checks:

1. https://github.com/kvesteri/sqlalchemy-utils/blob/master/sqlalchemy_utils/functions/orm.py#L811
2. https://github.com/kvesteri/sqlalchemy-utils/blob/master/sqlalchemy_utils/observer.py#L308

In both cases, the dict is treated as a sequence, is iterated over and converted into a list or set.

Note that the JSON column could also contain a list , so I think just ignoring dicts is not the right answer. Rather, there would need to be some knowledge about whether the value gotten from the model is from a relationship, or not.