Fix brandon-rhodes#15 by adding suggested (and correct) solution

Author: brandon-rhodes

Solutions-1.ipynb

@@ -1274,7 +1274,14 @@
     "\n",
     "c = cast\n",
     "c = c[c.character == 'Ophelia']\n",
-    "len(c)"
+    "len(c)\n",
+    "\n",
+    "# That was my original answer.\n",
+    "# But 9peppe on GitHub points out I am wrong! Instead:\n",
+    "\n",
+    "len(cast[cast.character == \"Ophelia\"].name.unique())\n",
+    "\n",
+    "# Can you work out why the two answers are different?"
    ]
   },
   {