[MRG] Add an example using validation curves (#203)
[MRG] Add an example using validation curves (#203)

* Add an example using validation cruves

* pep8

glemaitre/UnbalancedDataset,fmfn/UnbalancedDataset,fmfn/UnbalancedDataset,glemaitre/UnbalancedDataset,scikit-learn-contrib/imbalanced-learn,scikit-learn-contrib/imbalanced-learn