Fixed flake8 errors.

django/db/migrations/migration.py

@@ -129,6 +129,7 @@ class Migration(object):
             operation.database_backwards(self.app_label, schema_editor, from_state, to_state)
         return project_state
 
+
 def swappable_dependency(value):
     """
     Turns a setting value into a dependency.

tests/migrations/test_state.py

@@ -297,18 +297,21 @@ class StateTests(TestCase):
 
         class Author(models.Model):
             name = models.TextField()
+
             class Meta:
                 app_label = "migrations"
                 apps = new_apps
 
         class Book(models.Model):
             author = models.ForeignKey(Author)
+
             class Meta:
                 app_label = "migrations"
                 apps = new_apps
 
         class Magazine(models.Model):
             authors = models.ManyToManyField(Author)
+
             class Meta:
                 app_label = "migrations"
                 apps = new_apps