Update vendor dependencies

vendor/golang.org/x/oauth2/google/example_test.go

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build appenginevm appengine
-
 package google_test
 
 import (
@@ -12,6 +10,7 @@ import (
 	"log"
 	"net/http"
 
+	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
 	"golang.org/x/oauth2/jwt"
@@ -148,3 +147,16 @@ func ExampleComputeTokenSource() {
 	}
 	client.Get("...")
 }
+
+func ExampleCredentialsFromJSON() {
+	ctx := context.Background()
+	data, err := ioutil.ReadFile("/path/to/key-file.json")
+	if err != nil {
+		log.Fatal(err)
+	}
+	creds, err := google.CredentialsFromJSON(ctx, data, "https://www.googleapis.com/auth/bigquery")
+	if err != nil {
+		log.Fatal(err)
+	}
+	_ = creds // TODO: Use creds.
+}