fix(examples): correct typo in chat_calculator comment

Author: Rahul-Lashkari

site/en/examples/chat_calculator.ipynb

@@ -360,7 +360,7 @@
         "    return None, None\n",
         "  # keep everything before opening the calc tag.\n",
         "  text, remainder = result.split('<calc>', 1)\n",
-        "  # drop everything after closing the c alc tag.\n",
+        "  # drop everything after closing the calc tag.\n",
         "  expression, junk = remainder.split('</calc>', 1)\n",
         "\n",
         "  # Remove the units like \"7 cats / hour\" -> \"7\"\n",