def rstrip!
      if capture_position.nil?
        buffer.rstrip!
        return
      end

      buffer << buffer.slice!(capture_position..-1).rstrip
    end
def rstrip!
      if capture_position.nil?
        buffer.rstrip!
        return
      end

      buffer << buffer.slice!(capture_position..-1).rstrip
    end
Remove the whitespace from the right side of the buffer string.
 Doesn't do anything if we're at the beginning of a capture_haml block.