gource: 0.47 -> 0.48

Semi-automatic update. These checks were done:

- built on NixOS
- ran `/nix/store/gyy4z4wamcdzymm7q4a6j1dljxcad7w2-gource-0.48/bin/gource -h` got 0 exit code
- ran `/nix/store/gyy4z4wamcdzymm7q4a6j1dljxcad7w2-gource-0.48/bin/gource --help` got 0 exit code
- ran `/nix/store/gyy4z4wamcdzymm7q4a6j1dljxcad7w2-gource-0.48/bin/gource -h` and found version 0.48
- ran `/nix/store/gyy4z4wamcdzymm7q4a6j1dljxcad7w2-gource-0.48/bin/gource --help` and found version 0.48
- found 0.48 with grep in /nix/store/gyy4z4wamcdzymm7q4a6j1dljxcad7w2-gource-0.48
- found 0.48 in filename of file in /nix/store/gyy4z4wamcdzymm7q4a6j1dljxcad7w2-gource-0.48