Update plot_cross_validation.py

I think `LabelKFold` got renamed to `GroupKFold` in Scikit-Learn `0.18`

Author: yinleon

mglearn/plot_cross_validation.py

@@ -3,8 +3,8 @@
 
 
 def plot_label_kfold():
-    from sklearn.model_selection import LabelKFold
-    labels = [0, 0, 0, 1, 1, 1, 1, 2, 2, 3, 3, 3]
+    from sklearn.model_selection import GroupKFold
+    groups = [0, 0, 0, 1, 1, 1, 1, 2, 2, 3, 3, 3]
 
     plt.figure(figsize=(10, 2))
     plt.title("LabelKFold")
@@ -17,9 +17,9 @@ def plot_label_kfold():
     n_iter = 3
     n_samples_per_fold = 1
 
-    cv = LabelKFold(n_splits=3)
+    cv = GroupKFold(n_splits=3)
     mask = np.zeros((n_iter, n_samples))
-    for i, (train, test) in enumerate(cv.split(range(12), labels=labels)):
+    for i, (train, test) in enumerate(cv.split(range(12), groups=groups)):
         mask[i, train] = 1
         mask[i, test] = 2