Suppress warnings from skopt using deprecated sklearn API

[felker]

Closes #12. The warning is due to https://github.com/scikit-optimize/scikit-optimize still using the deprecated sklearn API as of skopt v0.5.2 (2018-03-25).

Discussed in scikit-optimize/scikit-optimize#774

They have two open PRs that address this, but they haven't been updated in months:

• Use joblib instead of sklearn.externals.joblib scikit-optimize/scikit-optimize#776
• [MRG] Allow BayesSearchCV to work with sklearn 0.21 scikit-optimize/scikit-optimize#777

[codecov]

Codecov Report

Merging #21 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #21   +/-   ##
=======================================
  Coverage   14.03%   14.03%           
=======================================
  Files         264      264           
  Lines       14536    14536           
  Branches     1907     1907           
=======================================
  Hits         2040     2040           
  Misses      12423    12423           
  Partials       73       73

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[Deathn0t]

Hi @felker, thank you for your contribution, it will be much less annoying.