def shift_argument
      if index = @entries.find_index { |type, _| type == :arg }
        entry = @entries[index]
        @entries.delete_at(index)
        entry.last
      end
    end
def shift_argument
      if index = @entries.find_index { |type, _| type == :arg }
        entry = @entries[index]
        @entries.delete_at(index)
        entry.last
      end
    end
@return [String] The first argument in the remaining parameters.

 @note   This will remove the argument from the remaining parameters.

 @example

   argv = CLAide::ARGV.new(['tea', 'white'])
   argv.shift_argument # => 'tea'
   argv.arguments      # => ['white']