Fixing date and time formatting when using additional formats

Fixing bug when formatting dates and times with additional format strings that would cause unexpected errors:

```ruby
irb(main):065:0> DateTime.now.localize(:es).to_date.to_additional_s('yMMMd')
ArgumentError: wrong number of arguments (2 for 1)
```

See [issue 49](https://github.com/twitter/twitter-cldr-js/issues/49).