To cite package 'aws.polly' in publications use:

Leeper TJ (2016). aws.polly: An R Package. R package version 0.1.2.1.

Corresponding BibTeX entry:

  @Manual{,
    title = {aws.polly: An R Package},
    author = {Thomas J. Leeper},
    year = {2016},
    note = {R package version 0.1.2.1},
  }