Support Ruby 3.0, verify SHA256 checksum of downloaded libpg_query (#178)
Support Ruby 3.0, verify SHA256 checksum of downloaded libpg_query (#178)

- Verify SHA256 checksum to guard against any malicious attempts to change the archive.
- Use `URI.open` to fix Ruby 3.0 support
lfittl/pg_query,lfittl/pg_query,jcsjcs/pg_query,jcsjcs/pg_query,jcsjcs/pg_query