When using blpop/brpop with only one parameter, the :exclude_last option in the COMMANDS table excludes the list_name from being prefixed

This code in the method_missing method excludes the last parameter of the called method

```ruby
when :exclude_last
  last = args.pop
  args = add_namespace(args)
  args.push(last) if last
```
This doesn't take into account that for the blpop and brpop commands, the timeout parameter is optional.

This means there is only 1 parameter, which therefore won't be prefixed, even though it is the list_name, which does need to be prefixed.

Tests still pass and example added to test this case.