Make notebooks 1 to 9 runnable in Colab without changes

06_decision_trees.ipynb

@@ -14,6 +14,17 @@
     "_This notebook contains all the sample code and solutions to the exercises in chapter 6._"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<table align=\"left\">\n",
+    "  <td>\n",
+    "    <a target=\"_blank\" href=\"https://colab.research.google.com/github/ageron/handson-ml2/blob/master/06_decision_trees.ipynb\"><img src=\"https://www.tensorflow.org/images/colab_logo_32px.png\" />Run in Google Colab</a>\n",
+    "  </td>\n",
+    "</table>"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -722,7 +733,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.4"
+   "version": "3.7.3"
   },
   "nav_menu": {
    "height": "309px",