To cite the ridge package, use:

Cule E, Moritz S (2019). ridge: Ridge Regression with Automatic Selection of the Penalty Parameter. R package version 2.4, https://CRAN.R-project.org/package=ridge.

Corresponding BibTeX entry:

  @Manual{,
    title = {ridge: Ridge Regression with Automatic Selection of the
      Penalty Parameter},
    author = {Erika Cule and Steffen Moritz},
    year = {2019},
    note = {R package version 2.4},
    url = {https://CRAN.R-project.org/package=ridge},
  }