poco: 1.7.8 -> 1.8.1

Semi-automatic update. These checks were performed:

- built on NixOS
- ran `/nix/store/i0mvrxm8vlgilmmkqrlp33g122iw5zlm-poco-1.8.1/bin/cpspc -h` got 0 exit code
- ran `/nix/store/i0mvrxm8vlgilmmkqrlp33g122iw5zlm-poco-1.8.1/bin/cpspc --help` got 0 exit code
- ran `/nix/store/i0mvrxm8vlgilmmkqrlp33g122iw5zlm-poco-1.8.1/bin/cpspc help` got 0 exit code
- ran `/nix/store/i0mvrxm8vlgilmmkqrlp33g122iw5zlm-poco-1.8.1/bin/f2cpsp -h` got 0 exit code
- ran `/nix/store/i0mvrxm8vlgilmmkqrlp33g122iw5zlm-poco-1.8.1/bin/f2cpsp --help` got 0 exit code
- ran `/nix/store/i0mvrxm8vlgilmmkqrlp33g122iw5zlm-poco-1.8.1/bin/f2cpsp help` got 0 exit code
- found 1.8.1 with grep in /nix/store/i0mvrxm8vlgilmmkqrlp33g122iw5zlm-poco-1.8.1

cc "@orivej"