postgrey: 1.36 -> 1.37

Semi-automatic update. These checks were performed:

- built on NixOS
- ran `/nix/store/axvpmnbhi27rca2476cj66mv1xk92w2f-postgrey-1.37/bin/postgrey --version` and found version 1.37
- found 1.37 with grep in /nix/store/axvpmnbhi27rca2476cj66mv1xk92w2f-postgrey-1.37
- found 1.37 in filename of file in /nix/store/axvpmnbhi27rca2476cj66mv1xk92w2f-postgrey-1.37