Adapt to migration of measures MLJBase -> StatisticalMeasures

[ablaom]

This PR needs:

• Replace built-in measures with measures in StatisticalMeasures.jl MLJBase.jl#909

In this PR we:

• (breaking) Adapt to the migration of measures out of MLJBase.jl and into StatisticalMeasures.jl

[codecov]

Codecov Report

Attention: 15 lines in your changes are missing coverage. Please review.

Comparison is base (2f501db) 79.27% compared to head (f25de30) 78.37%.

❗ Current head f25de30 differs from pull request most recent head c4aba20. Consider uploading reports for the commit c4aba20 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #30      +/-   ##
==========================================
- Coverage   79.27%   78.37%   -0.91%     
==========================================
  Files           2        3       +1     
  Lines         222      222              
==========================================
- Hits          176      174       -2     
- Misses         46       48       +2     

Files	Coverage Δ
src/MLJEnsembles.jl	100.00% <ø> (ø)
src/ensembles.jl	78.08% <48.27%> (-1.01%)	⬇️

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