update to remove chained indexing

https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy

Author: gregcaporaso

q2_sample_classifier/visuals.py

@@ -167,9 +167,9 @@ def _plot_confusion_matrix(y_test, y_pred, classes, normalize, palette,
     predictions.loc["Overall Accuracy"] = ""
     predictions.loc["Baseline Accuracy"] = ""
     predictions.loc["Accuracy Ratio"] = ""
-    predictions.loc["Overall Accuracy"]["Overall Accuracy"] = accuracy
-    predictions.loc["Baseline Accuracy"]["Overall Accuracy"] = basline_accuracy
-    predictions.loc["Accuracy Ratio"]["Overall Accuracy"] = accuracy_ratio
+    predictions.loc["Overall Accuracy", "Overall Accuracy"] = accuracy
+    predictions.loc["Baseline Accuracy", "Overall Accuracy"] = basline_accuracy
+    predictions.loc["Accuracy Ratio", "Overall Accuracy"] = accuracy_ratio
 
     return predictions, confusion