fix miss delimiter error

resources/definitions/anet3d.def.json

@@ -12,7 +12,7 @@
         
         "preferred_variant_name": "0.4mm Nozzle",
         "preferred_quality_type": "standard",
-        "preferred_material": "generic_pla"
+        "preferred_material": "generic_pla",
         "machine_extruder_trains":
         {
             "0": "anet3d_extruder_0"