Allow example app and tests to be run with Django 2.2 (django-json-api#642)

Author: sliverc

example/fixtures/blogentry.json

@@ -83,9 +83,7 @@
     "n_comments": 0,
     "n_pingbacks": 0,
     "rating": 0,
-    "authors": [
-      1
-    ]
+    "authors": []
   }
 },
 {
@@ -102,9 +100,7 @@
     "n_comments": 0,
     "n_pingbacks": 0,
     "rating": 0,
-    "authors": [
-      2
-    ]
+    "authors": []
   }
 },
 {

example/settings/dev.py

@@ -21,7 +21,6 @@
     'django.contrib.sites',
     'django.contrib.sessions',
     'django.contrib.auth',
-    'django.contrib.admin',
     'rest_framework',
     'polymorphic',
     'example',