format DOI in Links: as \doi{}

[ThierryO]

I'm having in the DESCRIPTION URL: https://doi.org/10.5281/zenodo.1485309

and in an R file the code below to generate a git2rdata-package.Rd

#' @keywords internal
"_PACKAGE"

The doi is formated as \url{https://doi.org/10.5281/zenodo.1485309} which yiels a NOTE on CRAN incoming feasibility

Found the following URLs which should use \doi (with the DOI name only):
  File 'git2rdata-package.Rd':
    https://doi.org/10.5281/zenodo.1485309