use markdown front matter instead of raw

Author: hamelsmu

nbs/tutorials/modular_nbdev.ipynb

@@ -1,15 +1,5 @@
 {
  "cells": [
-  {
-   "cell_type": "raw",
-   "id": "d3d59c9d-a2f2-4ee8-a05a-000d171aa01d",
-   "metadata": {},
-   "source": [
-    "---\n",
-    "skip_showdoc: true\n",
-    "---"
-   ]
-  },
   {
    "cell_type": "markdown",
    "id": "a2ed9821",
@@ -18,7 +8,8 @@
     "# Modular nbdev\n",
     "\n",
     "> How to use nbdev's various tools separately\n",
-    "- order: 9"
+    "- order: 9\n",
+    "- skip_showdoc: true"
    ]
   },
   {