Fix old chain backwardscompatibillity not applying properly

Author: TBlueF

core/src/main/resourceExtensions/pack.mcmeta

@@ -15,7 +15,7 @@
       },
       {
         "formats": { "min_inclusive": 67 },
-        "directory": "mc_1_21_9"
+        "directory": "mc1_21_9"
       }
     ]
   }