updated spam_example. not ready to merge: error with plotting negative values
updated spam_example. not ready to merge: error with plotting negative values

scikit-learn-contrib/forest-confidence-interval,arokem/sklearn-forest-ci,uwescience/sklearn-forest-ci,uwescience/sklearn-forest-ci,kpolimis/sklearn-forest-ci,arokem/sklearn-forest-ci,scikit-learn-contrib/forest-confidence-interval,kpolimis/sklearn-forest-ci