Update plt.grid args to avoid warning message

samples/core/tutorials/keras/basic_classification.ipynb

@@ -416,7 +416,7 @@
         "plt.figure()\n",
         "plt.imshow(train_images[0])\n",
         "plt.colorbar()\n",
-        "plt.grid('off')"
+        "plt.grid(False)"
       ],
       "execution_count": 0,
       "outputs": []
@@ -479,7 +479,7 @@
         "    plt.subplot(5,5,i+1)\n",
         "    plt.xticks([])\n",
         "    plt.yticks([])\n",
-        "    plt.grid('off')\n",
+        "    plt.grid(False)\n",
         "    plt.imshow(train_images[i], cmap=plt.cm.binary)\n",
         "    plt.xlabel(class_names[train_labels[i]])"
       ],
@@ -756,7 +756,7 @@
       "source": [
         "def plot_image(i, predictions_array, true_label, img):\n",
         "  predictions_array, true_label, img = predictions_array[i], true_label[i], img[i]\n",
-        "  plt.grid('off')\n",
+        "  plt.grid(False)\n",
         "  plt.xticks([])\n",
         "  plt.yticks([])\n",
         "  \n",
@@ -775,7 +775,7 @@
         "\n",
         "def plot_value_array(i, predictions_array, true_label):\n",
         "  predictions_array, true_label = predictions_array[i], true_label[i]\n",
-        "  plt.grid('off')\n",
+        "  plt.grid(False)\n",
         "  plt.xticks([])\n",
         "  plt.yticks([])\n",
         "  thisplot = plt.bar(range(10), predictions_array, color=\"#777777\")\n",