fix an admonition in brexit notebook

Author: drbenvincent

docs/source/notebooks/sc_pymc_brexit.ipynb

@@ -215,13 +215,9 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "<div class=\"alert alert-info\">\n",
-    "\n",
-    "Note:\n",
-    "\n",
+    ":::{note}\n",
     "The `random_seed` keyword argument for the PyMC sampler is not neccessary. We use it here so that the results are reproducible.\n",
-    "\n",
-    "</div>"
+    ":::"
    ]
   },
   {