$ go build github.com/user/hallo
 github.com/user/hallo/main.go:5:3: cannot find package "github.com/ogier/pflag" in any of:
         /usr/lib/go/src/github.com/ogier/pflag (from $GOROOT)
         /home/dominikh/go/src/github.com/ogier/pflag (from $GOPATH)