oauth2/google: change import paths

Change google.golang.org/cloud to cloud.google.com/go.

Change-Id: I6955a38ab97019d3d1dc094979e0ca2e45dea071
Reviewed-on: https://go-review.googlesource.com/25363
Reviewed-by: Chris Broadfoot <cbro@golang.org>
diff --git a/google/default.go b/google/default.go
index b952362..565d731 100644
--- a/google/default.go
+++ b/google/default.go
@@ -14,10 +14,10 @@
 	"path/filepath"
 	"runtime"
 
+	"cloud.google.com/go/compute/metadata"
 	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/jwt"
-	"google.golang.org/cloud/compute/metadata"
 )
 
 // DefaultClient returns an HTTP Client that uses the
diff --git a/google/google.go b/google/google.go
index 4e96fb6..82399b0 100644
--- a/google/google.go
+++ b/google/google.go
@@ -21,9 +21,9 @@
 	"strings"
 	"time"
 
+	"cloud.google.com/go/compute/metadata"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/jwt"
-	"google.golang.org/cloud/compute/metadata"
 )
 
 // Endpoint is Google's OAuth 2.0 endpoint.