`write.bib` does not write UTF-8 characters properly

Hi,

I have seen this when trying to create a bibtex file for cffr:

library(bibtex)
packageVersion("bibtex")

entry <- bibentry(
  "Article",
  doi = "10.21105/joss.03900",
  url = "https://doi.org/10.21105/joss.03900",
  year = 2021,
  publisher = "The Open Journal",
  volume = 6,
  number = 67,
  pages = 3900,
  author = person("Diego", "Hernangómez"),
  title = "cffr: Generate Citation File Format Metadata for R Packages",
  journal = "Journal of Open Source Software"
)

write.bib(entry)

But the "Rpackages.bib" file is:

@Article{,
  doi = {10.21105/joss.03900},
  url = {https://doi.org/10.21105/joss.03900},
  year = {2021},
  publisher = {The Open Journal},
  volume = {6},
  number = {67},
  pages = {3900},
  author = {Diego Hernang?mez},
  title = {cffr: Generate Citation File Format Metadata for R Packages},
  journal = {Journal of Open Source Software},
}

Note the author key: author = {Diego Hernang?mez},, not propley displayed.

ropensci / bibtex

`write.bib` does not write UTF-8 characters properly #43