explicitly converted error message to string

[tagomatech]

Python 3.5 -- Explicitly converted error message to string in the definition of the _get_imp() function, otherwise a type error is raised (TypeError: Can't convert 'ValueError' object to str implicitly). See str(e) below:

    def _get_imp(self, X, y):
        try:
            self.estimator.fit(X, y)
        except Exception as e:
            raise ValueError('Please check your X and y variable. The provided'
                             'estimator cannot be fitted to your data.\n' + str(e))
        try:
            imp = self.estimator.feature_importances_
        except Exception:
            raise ValueError('Only methods with feature_importance_ attribute '
                             'are currently supported in BorutaPy.')
        return imp

[danielhomola]

thanks!