Fix method signature for #options_value.

Fixes `api#options_value` method signature to allow for options.

Edit: API docs say "This GET request does not take any parameters" but this is a problem as the default limit is 50 values and as is, the method doesn't allow `limit` or `page` arguments.

`api.get_options_value(50, {:page => 2})` throws an `ArgumentError` (2 for 1)

So, as an example, if you have more than 50 colors for a color option... :shit: