[fix] Avoid default_app_config Deprecation Warning in Django >= 3.2 (#268)

* make conditional on django version

* [fix] Avoid default_app_config Deprecation Warning in Django >= 3.2

Django 3.2 started throwing deprecation warnings about the use of
default_app_config in modules' __init__.py. The practice will start
throwing errors in Django 4.1. This precludes future problems
by only including the code if the Django version is below 3.2.

* [fix] Flake8 formatting

Co-authored-by: Asif Saif Uddin <auvipy@gmail.com>

Author: bluppfisk

rest_framework_gis/__init__.py

@@ -1,3 +1,5 @@
+import django
+
 VERSION = (0, 18, 0, 'final')
 __version__ = VERSION  # alias
 
@@ -14,4 +16,5 @@ def get_version():
     return version
 
 
-default_app_config = 'rest_framework_gis.apps.AppConfig'
+if django.VERSION < (3, 2):
+    default_app_config = 'rest_framework_gis.apps.AppConfig'