Ranking Metrics Example - minor fix (#1517)

## Description

In the ranking metrics example, replace prediction to target in
multi-class relevance for single column case.

- [x] I have reviewed the [Guidelines for Contributing](CONTRIBUTING.md)
and the [Code of Conduct](CODE_OF_CONDUCT.md).

Co-authored-by: felipe207 <felipe@whylabs.ai>

python/examples/experimental/Writing_Ranking_Performance_Metrics_to_WhyLabs.ipynb

@@ -565,8 +565,8 @@
       "metadata": {},
       "outputs": [],
       "source": [
-        "# single prediction column\n",
-        "df_multi_single_column = pd.DataFrame({\"predictions\": [[3, 2, 3, 0, 1, 2, 3, 2]]})\n",
+        "# single target column\n",
+        "df_multi_single_column = pd.DataFrame({\"ranked_targets\": [[3, 2, 3, 0, 1, 2, 3, 2]]})\n",
         "\n",
         "# target + prediction columns\n",
         "\n",