herwig: 7.1.1 -> 7.1.2

Semi-automatic update. These checks were performed:

- built on NixOS
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/gosam2herwig -h` got 0 exit code
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/gosam2herwig --help` got 0 exit code
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/mg2herwig -h` got 0 exit code
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/mg2herwig --help` got 0 exit code
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/herwig-mergegrids -h` got 0 exit code
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/herwig-mergegrids --help` got 0 exit code
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/Herwig -h` got 0 exit code
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/Herwig --help` got 0 exit code
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/Herwig -V` and found version 7.1.2
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/Herwig --version` and found version 7.1.2
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/Herwig -h` and found version 7.1.2
- ran `/nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2/bin/Herwig --help` and found version 7.1.2
- found 7.1.2 with grep in /nix/store/wl85ali5l9g4naazpbkdlk3aqrlwi2g4-herwig-7.1.2

cc "@veprbl"