Uninitialized constant JiebaRb::Keyword::USER_DICT_FILE

[metacortex]

It raises error when I create JiebaRb::Keyword object with default user_dict option.

JiebaRb::Keyword.new user_dict: :default

https://github.com/altkatz/jieba_rb/blob/master/lib/jieba_rb.rb#L49

I think USER_DICT_FILE must be DEFAULT_USER_DICT.