fix GPU numbering

ColorizeTrainingVideo.ipynb

@@ -23,7 +23,7 @@
    "outputs": [],
    "source": [
     "import os\n",
-    "os.environ['CUDA_VISIBLE_DEVICES']='2' "
+    "os.environ['CUDA_VISIBLE_DEVICES']='0' "
    ]
   },
   {

ImageColorizer.ipynb

@@ -7,7 +7,7 @@
    "outputs": [],
    "source": [
     "import os\n",
-    "os.environ['CUDA_VISIBLE_DEVICES']='1' "
+    "os.environ['CUDA_VISIBLE_DEVICES']='0' "
    ]
   },
   {

ImageColorizerArtisticTests.ipynb

@@ -7,7 +7,7 @@
    "outputs": [],
    "source": [
     "import os\n",
-    "os.environ['CUDA_VISIBLE_DEVICES']='2' "
+    "os.environ['CUDA_VISIBLE_DEVICES']='0' "
    ]
   },
   {