FeatureSelector is still exported

[adwasser]

It looks like the FeatureSelector transformation was moved to a different package in this PR:

#558

But the symbol is still exported

MLJModels.jl/src/MLJModels.jl

Line 46 in 320a29c

export FeatureSelector, UnivariateDiscretizer,

which leads to a confusing user error:

UndefVarError: `FeatureSelector` not defined

[ablaom]

Good catch, thanks!