Use upstream version of pg_query again

The upstream gem has incorporated all the necessary changes--namely ARM
support and SHA256 verification of libpg_query--so we can now switch
back to the official gem.

CHANGELOG: https://github.com/lfittl/pg_query/blob/master/CHANGELOG.md

Diff: https://github.com/lfittl/pg_query/compare/v1.2.0..v1.3.0