fix: count the Marathon data trees as game data

bios/Bungie holds the Marathon scenarios Aleph One reads, entries its profile files as category game_data. Listed with the other publishers' trees, they leave the system files count and sit under Game engines and PC games on the site.

mkdocs.yml

@@ -158,7 +158,6 @@ nav:
       - Bandai: systems/bandai.md
       - BBK: systems/bbk.md
       - Bit Corporation: systems/bit-corporation.md
-      - Bungie: systems/bungie.md
       - Camputers: systems/camputers.md
       - Casio: systems/casio.md
       - Coleco: systems/coleco.md
@@ -225,6 +224,7 @@ nav:
       - 3D Realms: systems/3d-realms.md
       - Apogee: systems/apogee.md
       - Blizzard: systems/blizzard.md
+      - Bungie: systems/bungie.md
       - Dinothawr: systems/dinothawr.md
       - Electronic Arts: systems/electronic-arts.md
       - Epic MegaGames: systems/epic-megagames.md