LiblineaR penalty does *not* allow submodel "trick"

[juliasilge]

Closes #551

The penalty (cost) for the LiblineaR engine of logistic_reg() does not allow for the submodel "trick".

library(tidymodels)
#> Registered S3 method overwritten by 'tune':
#>   method                   from   
#>   required_pkgs.model_spec parsnip
data(lending_club)
folds <- vfold_cv(lending_club, v = 5)

spec <- logistic_reg(penalty = tune()) %>% 
  set_engine("LiblineaR") %>% 
  set_mode("classification")

tune_grid(
  spec,
  Class ~ int_rate,
  resamples = folds,
  grid = 3
)
#> # Tuning results
#> # 5-fold cross-validation 
#> # A tibble: 5 × 4
#>   splits              id    .metrics         .notes          
#>   <list>              <chr> <list>           <list>          
#> 1 <split [7885/1972]> Fold1 <tibble [6 × 5]> <tibble [0 × 1]>
#> 2 <split [7885/1972]> Fold2 <tibble [6 × 5]> <tibble [0 × 1]>
#> 3 <split [7886/1971]> Fold3 <tibble [6 × 5]> <tibble [0 × 1]>
#> 4 <split [7886/1971]> Fold4 <tibble [6 × 5]> <tibble [0 × 1]>
#> 5 <split [7886/1971]> Fold5 <tibble [6 × 5]> <tibble [0 × 1]>

^{Created on 2021-09-13 by the reprex package (v2.0.1)}

[topepo]

Looks good!

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