STYLE: Call itk.ParameterObject.WriteParameterFile the static way

Follow-up to pull request #351 commit 6d377a2 "STYLE: Call `itk.ParameterObject.GetDefaultParameterMap` the static way"

Author: N-Dekker

examples/ITK_Example02_CustomOrMultipleParameterMaps.ipynb

@@ -228,14 +228,14 @@
    "outputs": [],
    "source": [
     "# Save custom parameter map\n",
-    "parameter_object.WriteParameterFile(\n",
+    "itk.ParameterObject.WriteParameterFile(\n",
     "    parameter_map_custom, \"exampleoutput/parameters_custom.txt\"\n",
     ")\n",
     "\n",
     "# Or serialize each parameter map to a file.\n",
     "for index in range(parameter_object.GetNumberOfParameterMaps()):\n",
     "    parameter_map = parameter_object.GetParameterMap(index)\n",
-    "    parameter_object.WriteParameterFile(\n",
+    "    itk.ParameterObject.WriteParameterFile(\n",
     "        parameter_map, \"exampleoutput/Parameters.{0}.txt\".format(index)\n",
     "    )"
    ]