Add internal classes and add type hints + mypy.

tests/test_project/app_ignore_migration/migrations/0001_initial.py

@@ -1,5 +1,7 @@
 # Generated by Django 2.1.4 on 2019-03-21 20:40
 
+from __future__ import annotations
+
 from django.db import migrations, models
 
 

tests/test_project/app_ignore_migration/migrations/0002_ignore_migration.py

@@ -1,5 +1,7 @@
 # Generated by Django 2.1.4 on 2019-03-21 20:41
 
+from __future__ import annotations
+
 from django.db import migrations, models
 
 import django_migration_linter as linter

tests/test_project/app_ignore_migration/models.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from django.db import models