revert deleted code

Problem described here: https://github.com/dataquestio/solutions/commit/e606e3294ace372adf0ecc2d6f2a6c0de8a5ca93#r36447398

Mission310Solutions.ipynb

@@ -1942,7 +1942,11 @@
     }
    ],
    "source": [
-    "=;"
+    "# Remove the rows with null values in 'CountryLive'\n",
+    "fcc_good = fcc_good[fcc_good['CountryLive'].notnull()]\n",
+    "\n",
+    "# Frequency table to check if we still have enough data\n",
+    "fcc_good['CountryLive'].value_counts().head()"
    ]
   },
   {