address graphviz issue

Author: jphall663

dt_surrogate_loco.ipynb

@@ -652,7 +652,7 @@
     "print('Calling external process ...')\n",
     "print(' '.join(gv_args))\n",
     "# if the line below is failing for you, try instead:\n",
-    "# _ = subprocess.call(png_args, shell=True)  \n",
+    "# _ = subprocess.call(gv_args, shell=True)  \n",
     "_ = subprocess.call(gv_args)"
    ]
   },
@@ -688,6 +688,8 @@
     "# call\n",
     "print('Calling external process ...')\n",
     "print(' '.join(png_args))\n",
+    "# if the line below is failing for you, try instead:\n",
+    "# _ = subprocess.call(png_args, shell=True)  \n",
     "_ = subprocess.call(png_args)"
    ]
   },