config_test.go.TestNewDefaultWithXDGConfigHome fails on macOS #196

The test config_test.go.TestNewDefaultWithXDGConfigHome fails on any non linux based (or BSD) system as go respects the macOS/Windows default config folders (~/Library/Application\ Support/ and %AppData% respectively), or rather it ignores XDG_CONFIG_HOME on those systems.

Seeing as nom also repsects this I think this could be fixed by just skipping the tests on any environment that's not linux/bsd based

if runtime.GOOS != "linux" && runtime.GOOS != "freebsd"{
  t.Skip("XDG_CONFIG_HOME only supported on linux/BSD")
}

Happy to open up a pr if there aren't any other suggestions?