Update Python version

packages/toc/notebooks/demo.ipynb

@@ -982,7 +982,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.6.7"
+   "version": "3.7.3"
   },
   "toc-autonumbering": false,
   "toc-showcode": false,