Update tutorial.ipynb

Use `sh` instead of `shell` for consistent pre-formatted code formatting.

Author: dijonkitchen

nbs/tutorials/tutorial.ipynb

@@ -605,7 +605,7 @@
    "source": [
     "You should now create your package from your notebook by running:\n",
     "\n",
-    "```shell\n",
+    "```sh\n",
     "nbdev_export\n",
     "```\n",
     "\n",