install_deps() fails on travis on mac: 'missing value where TRUE/FALSE needed'

[maurolepore]

Thanks a LOT for remotes and support for R on Travis CI

On Travis CI with R 3.5.2 and macOS High Sierra I get this error (job):

> devtools::install_deps(dep = T, dependencies = TRUE, repos = c("https://cloud.r-project.org", "http://forestgeo.github.io/drat"))
fgeo.x (1.1.2 -> NA) [local]
Error in if (!file.info(path)$isdir) { : 
  missing value where TRUE/FALSE needed
Calls: <Anonymous> ... update.package_deps -> install_remotes -> vapply -> FUN -> source_pkg
In addition: Warning message:
In file.copy(x$path, bundle, recursive = TRUE) :
  problem copying /Users/usernlivt8Gy/fgeo.x_1.1.2.tar.gz to /var/folders/nz/vv4_9tw56nv9k3tkvyszvwg80000gn/T//RtmpzwHcLq/file14a516eb0ad54/fgeo.x_1.1.2.tar.gz: No such file or directory

The package passes rhub::check_on_macos() cleanly, and passes on Ubuntu on Travis, win-builder.

Locally, the isolated function call does what I expect:

[jimhester]

I think at least part of this is addressed by e473d9