Fixed a couple of deprecation warnings

from itertools import chain

from django.contrib.admin.util import get_fields_from_path, NotRelationField

from django.contrib.admin.utils import get_fields_from_path, NotRelationField

from django.core import checks

from django.db import models

from django.db.models.fields import FieldDoesNotExist

from __future__ import unicode_literals

from django.utils import six

from django.apps import apps

def check_generic_foreign_keys(**kwargs):

    from .generic import GenericForeignKey

    from django.db import models

    errors = []

    fields = (obj

        for cls in models.get_models()

        for cls in apps.get_models()

        for obj in six.itervalues(vars(cls))

        if isinstance(obj, GenericForeignKey))

    for field in fields: