marker update claims there are arguments even if none are given

```
marker update<Enter>
```
```
Traceback (most recent call last):
  File "/home/pawel/.marker/bin/marker", line 65, in <module>
    parse_arguments()
  File "/home/pawel/.marker/bin/marker", line 31, in parse_arguments
    return args.func(args)
TypeError: cmd_update() takes no arguments (1 given)
```