Fix bug in mini batch kmeans example

Author: zhengqm

examples/cluster/plot_mini_batch_kmeans.py

@@ -103,7 +103,7 @@
 different = (mbk_means_labels == 4)
 ax = fig.add_subplot(1, 3, 3)
 
-for l in range(n_clusters):
+for k in range(n_clusters):
     different += ((k_means_labels == k) != (mbk_means_labels == order[k]))
 
 identic = np.logical_not(different)