Fixing results directory reference

DeOldify_colab.ipynb

@@ -525,7 +525,7 @@
     "#This tends to be the case with the oldest photos.\n",
     "render_factor=42\n",
     "filters = [Colorizer(gpu=0, weights_path=weights_path)]\n",
-    "vis = ModelImageVisualizer(filters, render_factor=render_factor, results_dir='result_images')"
+    "vis = ModelImageVisualizer(filters, render_factor=render_factor, results_dir=results_dir)"
    ]
   },
   {