go.sys: use golang.org/x/... import paths

LGTM=bradfitz, rsc
R=rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/171050043
diff --git a/unix/mmap_unix_test.go b/unix/mmap_unix_test.go
index 5dfa75d..04d5720 100644
--- a/unix/mmap_unix_test.go
+++ b/unix/mmap_unix_test.go
@@ -9,7 +9,7 @@
 import (
 	"testing"
 
-	"code.google.com/p/go.sys/unix"
+	"golang.org/x/sys/unix"
 )
 
 func TestMmap(t *testing.T) {