Fix preferred quality type

The quality type 'fast' doesn't exist for Deltacomb. I'm going to be choosing a quality type that is available for this printer which has the name 'Fast', which is quality type 'd'.

resources/definitions/deltacomb_base.def.json

@@ -12,9 +12,9 @@
         "has_machine_quality":             true,
         "has_materials":                   true,
         "has_variants":                    true,
-        "variants_name":                   "Head",        
+        "variants_name":                   "Head",
         
-        "preferred_quality_type":          "fast",
+        "preferred_quality_type":          "d",
         "preferred_material":              "generic_pla",
         
         "machine_extruder_trains": {

resources/definitions/deltacomb_dc20flux.def.json

@@ -13,7 +13,7 @@
             "1": "deltacomb_dc20flux_extruder_1",
             "2": "deltacomb_dc20flux_extruder_2",
             "3": "deltacomb_dc20flux_extruder_3"
-	      }
+          }
     },
 
     "overrides": {

resources/definitions/deltacomb_dc21flux.def.json

@@ -13,7 +13,7 @@
             "1": "deltacomb_dc20flux_extruder_1",
             "2": "deltacomb_dc20flux_extruder_2",
             "3": "deltacomb_dc20flux_extruder_3"
-	      }
+          }
     },
 
     "overrides": {

resources/definitions/deltacomb_dc30flux.def.json

@@ -13,7 +13,7 @@
             "1": "deltacomb_dc30flux_extruder_1",
             "2": "deltacomb_dc30flux_extruder_2",
             "3": "deltacomb_dc30flux_extruder_3"
-	      }
+          }
     },
 
     "overrides": {