gmtp: 1.3.10 -> 1.3.11

Semi-automatic update. These checks were done:

- built on NixOS
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 1.3.11 with grep in /nix/store/8lp6lwxfy7zq94jd2f26vgxc1zs0scfm-gmtp-1.3.11
- found 1.3.11 in filename of file in /nix/store/8lp6lwxfy7zq94jd2f26vgxc1zs0scfm-gmtp-1.3.11