Update creality_ender3.def.json

I suggest a change to the value of max  Z-axis Jerk to be the same as on Marlin 1.1.9 firmware used by Ender 3. Its a small change, reducing 0,4 to 0,3. Having these settings match the firmware's configuration makes a print's estimated time more accurate.

resources/definitions/creality_ender3.def.json

@@ -59,6 +59,9 @@
         "jerk_travel": {
             "value": "jerk_print"
         },
+        "machine_max_jerk_z": {
+            "default_value": 0.3,
+        },
         "layer_height_0": {
             "default_value": 0.2
         },