typos: remove extra s's

grammatical agreement
tweak to more natural version
Fix wrong attribute doc in BaggingRegressor.
Merge pull request #3667 from ajschumacher/patch-6

typos: remove extra s's
Sample weights for gradient boosting

Exponential loss for classification + predict_proba refactoring
more tests
add exponential loss to narrative documentation
cosmit: doc
raise ValueError for sample_weights and robust regression
bincount supports weights
more elegant PriorProbabilityEstimator
adressed Olivier's feedback
update tests for new exception types
sample weight support for robust regression via weighted percentile algo
fix: consider sample_weights in robost init estimator and negative_gradient
fix: add **kwargs to Multinomial loss' negative_gradient
more tests for weighted percentile
cosmit
add GBRT sample weights to whats new