JSON fix: making max gradual infill steps lower to allow for engine not crashing when setting the infill to a low percentage (CURA-836)

resources/definitions/fdmprinter.def.json

@@ -1014,7 +1014,7 @@
                     "type": "int",
                     "minimum_value": "0",
                     "maximum_value_warning": "4",
-                    "maximum_value": "19",
+                    "maximum_value": "17",
                     "settable_per_mesh": true
                 },
                 "gradual_infill_step_height":