Patch db_migrate.py to always use the 'db' command

This means you can (have to) use the Flask-Migrate commands directly:
"./db_migrate.py stamp head" etc instead of "./db_migrate.py db stamp head"

db_migrate.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 # -*- coding: utf-8 -*-
+import sys
 from nyaa import app, db
 from flask_script import Manager
 from flask_migrate import Migrate, MigrateCommand
@@ -10,4 +11,12 @@ manager = Manager(app)
 manager.add_command("db", MigrateCommand)
 
 if __name__ == "__main__":
+	# Patch sys.argv to default to 'db'
+	argv_contents = sys.argv[:]
+	
+	sys.argv.clear()
+	sys.argv.append(argv_contents[0])
+	sys.argv.append('db')
+	sys.argv.extend(argv_contents[1:])
+
 	manager.run()