add x label to boxplot

Author: fritshermans

examples/cross_validation/plot_instance_hardness_cv.py

@@ -77,5 +77,6 @@
 # %%
 plt.boxplot([skf_result['test_score'], ih_result['test_score']],
             tick_labels=["StratifiedKFold", "InstanceHardnessCV"], vert=False)
+plt.xlabel('Average precision')
 plt.tight_layout()
 plt.show()