use the new django bigautofield, fixes a warning

axes/apps.py

@@ -7,6 +7,7 @@ log = getLogger(__name__)
 
 
 class AppConfig(apps.AppConfig):
+    default_auto_field = "django.db.models.BigAutoField"
     name = "axes"
     initialized = False
 

axes/migrations/0007_auto_20210606_2037.py

@@ -0,0 +1,23 @@
+# Generated by Django 3.2.4 on 2021-06-06 20:37
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('axes', '0006_remove_accesslog_trusted'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='accessattempt',
+            name='id',
+            field=models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID'),
+        ),
+        migrations.AlterField(
+            model_name='accesslog',
+            name='id',
+            field=models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID'),
+        ),
+    ]