Updating platform_offset for BQ printers

Fixes the reason why the Cura UI freezes when choosing my printer from
the wizard.

resources/definitions/bq_hephestos.def.json

@@ -10,13 +10,7 @@
         "category": "Other",
         "file_formats": "text/x-gcode",
         "platform": "bq_hephestos_platform.stl",
-        "platform_offset": {
-            "value": [
-                0,
-                -82,
-                0
-            ]
-        }
+        "platform_offset": [ 0, -82, 0]
     },
 
     "overrides": {