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

LGTM=bradfitz
R=rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/167190043

openpgp/s2k/s2k.go

@@ -12,7 +12,7 @@ import (
 	"io"
 	"strconv"
 
-	"code.google.com/p/go.crypto/openpgp/errors"
+	"golang.org/x/crypto/openpgp/errors"
 )
 
 // Config collects configuration parameters for s2k key-stretching

openpgp/s2k/s2k_test.go

@@ -15,7 +15,7 @@ import (
 	"encoding/hex"
 	"testing"
 
-	_ "code.google.com/p/go.crypto/ripemd160"
+	_ "golang.org/x/crypto/ripemd160"
 )
 
 var saltedTests = []struct {