Fixed post image migration saving posts when it's unnecessary

boards/migrations/0027_image_field_to_model.py

@@ -23,8 +23,8 b' class Migration(DataMigration):'
 
                 image.save()
 
+                post.images.clear()
                 post.images.add(image)
-                post.save()
 
     def backwards(self, orm):
         "Write your backwards methods here."