provider#node#can_inspect will fail on some systems because it is common
to have old node versions in OS (any Linux OS that has LTS releases)
and CI (Travis, Appveyor).
NODE_PATH can be trivially set with VimL.
Build scripts don't have to set it for the nodejs tests to work.
NODE_PATH is optional to begin with and is used only as a workaround
for the neovim node.js host.