To cite animation in publications use:

  Yihui Xie (2013). animation: An R Package for Creating Animations and
  Demonstrating Statistical Methods. Journal of Statistical Software,
  53(1), 1-27. URL https://doi.org/10.18637/jss.v053.i01.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{animation}: An {R} Package for Creating Animations and Demonstrating Statistical Methods},
    author = {Yihui Xie},
    journal = {Journal of Statistical Software},
    year = {2013},
    volume = {53},
    number = {1},
    pages = {1--27},
    url = {https://doi.org/10.18637/jss.v053.i01},
  }

  Yihui Xie [aut, cre], Christian Mueller [ctb], Lijia Yu [ctb],
  Weicheng Zhu [ctb] (). animation: A Gallery of Animations in
  Statistics and Utilities to Create Animations. R package version
  2.7.1.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {animation: A Gallery of Animations in Statistics and Utilities to Create
Animations},
    author = {Yihui Xie and Christian Mueller and Lijia Yu and Weicheng Zhu},
    note = {R package version 2.7.1},
    url = {https://yihui.org/animation/},
  }