ModuleNotFoundError : No module named 'sklearn.externals.six'

Question

dot_data = StringIO()  
tree.export_graphviz(clf, out_file=dot_data,  
                         feature_names=features)  
graph = pydotplus.graph_from_dot_data(dot_data.getvalue())  
Image(graph.create_png())

I am trying to make a decision tree, but i am having an of no module named sklearn.sixternal.six