Fixing small bug in Unitconverters tutorial

Author: erikvansebille

docs/user_guide/examples/tutorial_unitconverters.ipynb

@@ -296,7 +296,7 @@
     "kh_meridional_field = parcels.Field(\n",
     "    \"Kh_meridional\",\n",
     "    ds[\"Kh_meridional\"],\n",
-    "    grid=grid,\n",
+    "    grid=fieldset.U.grid,\n",
     "    interp_method=parcels.interpolators.XLinear,\n",
     ")\n",
     "\n",