registering clean command with app

Author: dantownsend

piccolo/apps/migrations/piccolo_app.py

@@ -1,12 +1,13 @@
 from piccolo.conf.apps import AppConfig
 from .commands.backwards import backwards
 from .commands.check import check
+from .commands.clean import clean
 from .commands.forwards import forwards
 from .commands.new import new
 
 
 APP_CONFIG = AppConfig(
     app_name="migrations",
     migrations_folder_path="",
-    commands=[backwards, check, forwards, new],
+    commands=[backwards, check, clean, forwards, new],
 )