Missing link to utils::winProgressBar

In my R function documentation I reference utils::winProgressBar as \code{\link[utils]{winProgressBar}}. This works as expected on my Windows development system, and also when I use devtools::check_win_release() to check it on a different Windows system. However, in travis-CI, the build fails with the message:

checking Rd cross-references ... WARNING
Missing link or links in documentation object 'TrajsMergeStats.Rd':
See section 'Cross-references' in the 'Writing R Extensions' manual.

I have tried both \code{\link[utils]{winProgressBar}} and \code{\link{winProgressBar}}, and both produce the same error, (of course the function name varies in the error message, being either [utils]{winProgressBar} or {winProgressBar}.

utils::winProgressBar() does not exist on non-windows systems, the easiest thing to do would be to omit linking to the function, but you can also use platform specific documentation for the link.