OSX warnings

```sh
XXXXXXXX:xxxxxxxxxxxxx$ go run main.go
# command-line-arguments
ld: warning: object file (/var/folders/3x/lhcndvw129gfrg6y17sg21xc0000gp/T/go-link-399631299/000024.o) was built for newer OSX version (10.11) than being linked (10.8)
ld: warning: object file (/var/folders/3x/lhcndvw129gfrg6y17sg21xc0000gp/T/go-link-399631299/000025.o) was built for newer OSX version (10.11) than being linked (10.8)
ld: warning: object file (/var/folders/3x/lhcndvw129gfrg6y17sg21xc0000gp/T/go-link-399631299/000026.o) was built for newer OSX version (10.11) than being linked (10.8)
ld: warning: object file (/var/folders/3x/lhcndvw129gfrg6y17sg21xc0000gp/T/go-link-399631299/000027.o) was built for newer OSX version (10.11) than being linked (10.8)
ld: warning: object file (/var/folders/3x/lhcndvw129gfrg6y17sg21xc0000gp/T/go-link-399631299/000028.o) was built for newer OSX version (10.11) than being linked (10.8)
ld: warning: object file (/var/folders/3x/lhcndvw129gfrg6y17sg21xc0000gp/T/go-link-399631299/000029.o) was built for newer OSX version (10.11) than being linked (10.8)
ld: warning: object file (/var/folders/3x/lhcndvw129gfrg6y17sg21xc0000gp/T/go-link-399631299/000030.o) was built for newer OSX version (10.11) than being linked (10.8)
ld: warning: object file (/var/folders/3x/lhcndvw129gfrg6y17sg21xc0000gp/T/go-link-399631299/000031.o) was built for newer OSX version (10.11) than being linked (10.8)
ld: warning: object file (/var/folders/3x/lhcndvw129gfrg6y17sg21xc0000gp/T/go-link-399631299/000032.o) was built for newer OSX version (10.11) than being linked (10.8)
ld: warning: object file (/Users/xxxxxxxx/go/src/github.com/andlabs/ui/libui_darwin_amd64.a(libui-combined.o)) was built for newer OSX version (10.12) than being linked (10.8)
```

Actual MacOS version: 10.13.6 64-bit
Go version: 1.11