gfan: 0.6 -> 0.6.2

Semi-automatic update. These checks were done:

- built on NixOS
- ran `/nix/store/gdzrfmvi5x26is0hbv0yyg5s61cxm7dy-gfan-0.6.2/bin/gfan --help` got 0 exit code
- found 0.6.2 with grep in /nix/store/gdzrfmvi5x26is0hbv0yyg5s61cxm7dy-gfan-0.6.2
- found 0.6.2 in filename of file in /nix/store/gdzrfmvi5x26is0hbv0yyg5s61cxm7dy-gfan-0.6.2