simplify FlipText Goodie using Text::UpsideDown

Seems to allow better handling of unicode/utf8.

In light of https://github.com/duckduckgo/p5-app-duckpan/issues/96 I was investigating if the problem was caused by DuckPAN (maybe it should handle the unicode better?) or if it was caused by the Goodie itself.

I noticed CPAN had a "Text::UpsideDown" package with had some upvotes and tried it out (also made the Goodie was smaller/simpler). It seemed to fix the broken output in DuckPAN Query and Server so I've submitted the changes.

//cc @jagtalon