Update retrieving the current branch name (#141)

Author: jackton1

migration_fixer/management/commands/makemigrations.py

@@ -104,7 +104,7 @@ def handle(self, *app_labels, **options):
                     if self.verbosity >= 2:
                         self.stdout.write("Retrieving the current branch...")
 
-                    current_branch = self.repo.head.ref.name
+                    current_branch = self.repo.active_branch.name
 
                     if self.repo.is_dirty():  # pragma: no cover
                         raise CommandError(