libpqxx: 6.1.0 -> 6.1.1

Semi-automatic update generated by https://github.com/ryantm/nix-update tools. These checks were done:

- built on NixOS
- ran `/nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1/bin/pqxx-config -h` got 0 exit code
- ran `/nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1/bin/pqxx-config --help` got 0 exit code
- ran `/nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1/bin/pqxx-config help` got 0 exit code
- ran `/nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1/bin/pqxx-config -V` and found version 6.1.1
- ran `/nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1/bin/pqxx-config -v` and found version 6.1.1
- ran `/nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1/bin/pqxx-config --version` and found version 6.1.1
- ran `/nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1/bin/pqxx-config version` and found version 6.1.1
- ran `/nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1/bin/pqxx-config -h` and found version 6.1.1
- ran `/nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1/bin/pqxx-config --help` and found version 6.1.1
- ran `/nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1/bin/pqxx-config help` and found version 6.1.1
- found 6.1.1 with grep in /nix/store/kk2j3iz4kllp58v3k0jy88pr78gqb53d-libpqxx-6.1.1
- directory tree listing: https://gist.github.com/5915a75a4c094a7918ab2b42fc150b80