Upgrade peg to peggy

Over in https://github.com/phetsims/phet-io-wrappers/issues/555, the PhET-iO team is using the browser-side runnable of peggy (the new pegjs library) for parsing a PhET-iO state-related grammar. It would be nice to have the same version for both of these usages of the grammar parser. I don't know how to upgrade or test the kite one though, so I'll log an issue. 