Fix "eval in closed module" issue

[ablaom]

IQVIA-ML/LightGBM.jl#71

[codecov-io]

Codecov Report

Merging #71 into dev will increase coverage by 7.33%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev      #71      +/-   ##
==========================================
+ Coverage   91.70%   99.04%   +7.33%     
==========================================
  Files           9        9              
  Lines         205      209       +4     
==========================================
+ Hits          188      207      +19     
+ Misses         17        2      -15     

Impacted Files	Coverage Δ
src/model_def.jl	100.00% <100.00%> (ø)
src/equality.jl	100.00% <0.00%> (ø)
src/metadata_utils.jl	100.00% <0.00%> (ø)
src/model_traits.jl	100.00% <0.00%> (+41.37%)	⬆️
src/parameter_inspection.jl	100.00% <0.00%> (+50.00%)	⬆️

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