fix lint errors

judge/migrations/0098_default_changes.py

@@ -1,8 +1,8 @@
 # Generated by Django 2.2.9 on 2020-01-23 21:36
 
 import django.core.validators
-from django.db import migrations, models
 import django.db.models.deletion
+from django.db import migrations, models
 
 
 class Migration(migrations.Migration):

judge/migrations/0100_custom_checker.py

@@ -1,6 +1,6 @@
 # Generated by Django 2.2.9 on 2020-01-23 22:28
-
 from django.db import migrations, models
+
 import judge.models.problem_data
 import judge.utils.problem_data
 

judge/models/problem_data.py

@@ -46,7 +46,10 @@ class ProblemData(models.Model):
     checker = models.CharField(max_length=10, verbose_name=_('checker'), choices=CHECKERS, blank=True)
     checker_args = models.TextField(verbose_name=_('checker arguments'), blank=True,
                                     help_text=_('checker arguments as a JSON object'))
-    custom_checker = models.FileField(verbose_name=_('custom checker file'), storage=problem_data_storage, null=True, blank=True,
+    custom_checker = models.FileField(verbose_name=_('custom checker file'),
+                                      storage=problem_data_storage,
+                                      null=True,
+                                      blank=True,
                                       upload_to=problem_directory_file,
                                       validators=[FileExtensionValidator(allowed_extensions=['py'])])
     __original_zipfile = None