context argument has been removed from the Field.from_db_value()

[psilva1982]

Hello,

The ImageCropField type is no longer working as of Django version 3x. The context argument has been removed from the Field.from_db_value() method. The details can be seen in docs. So if you agree, I'd like to contribute this little fix. It would help me a lot to maintain compatibility with some of my legacy systems.

# imagekit_cropper/fields.py

... 
    def from_db_value(self, value, expression, connection, context=None):
        return self.parse_value(value)
...