detect_os do not work on windows

[cderv]

Hi,

Digging into R-hub ecosytem and all its 📦 , I tried several things. When experimenting with sysreqs, it did not worked on windows because of an issue in detect_os

sysreqs:::detect_os()
#> Error in sysreqs:::detect_os(): sysreqs is not supported on your platform

Issue comes from os_type that is not handle correctly in detect_os which wants "win" not "windows"

sysreqs:::os_type()
#> [1] "windows"

Created on 2018-02-17 by the reprex package (v0.2.0).

[gaborcsardi]

Note that this is mostly cosmetics, as sysreqs does not do anything on windows, really.

[cderv]

I know but I have windows computer and found this. so I thought that it was worth fixing... for cosmetic mainly I agree.

Thanks for all the great work by the way.