fix heading levels

Author: afeld

lecture_1_demo_solutions.ipynb

@@ -1191,7 +1191,13 @@
   {
    "cell_type": "code",
    "execution_count": 8,
-   "metadata": {},
+   "metadata": {
+    "editable": true,
+    "slideshow": {
+     "slide_type": ""
+    },
+    "tags": []
+   },
    "outputs": [
     {
      "data": {
@@ -1299,7 +1305,7 @@
     "tags": []
    },
    "source": [
-    "#### Which complaints are most common?"
+    "### Which complaints are most common?"
    ]
   },
   {
@@ -1424,7 +1430,9 @@
     }
    ],
    "source": [
-    "complaint_counts = requests_clean.groupby(\"Complaint Type\").size().reset_index(name=\"count\")\n",
+    "complaint_counts = (\n",
+    "    requests_clean.groupby(\"Complaint Type\").size().reset_index(name=\"count\")\n",
+    ")\n",
     "complaint_counts"
    ]
   },
@@ -1452,7 +1460,7 @@
     "tags": []
    },
    "source": [
-    "#### What's the most frequent request per agency?\n",
+    "### What's the most frequent request per agency?\n",
     "\n",
     "First, create a DataFrame that contains the count of complaints per `Agency` per `Complaint Type`."
    ]