Update dependencies

Among others, this updates minio-go, so that the new "eu-west-3" zone
for AWS is supported.

vendor/cloud.google.com/go/internal/testutil/context.go

@@ -16,6 +16,7 @@
 package testutil
 
 import (
+	"fmt"
 	"io/ioutil"
 	"log"
 	"os"
@@ -23,6 +24,7 @@ import (
 	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
+	"golang.org/x/oauth2/jwt"
 )
 
 const (
@@ -59,13 +61,35 @@ func TokenSourceEnv(ctx context.Context, envVar string, scopes ...string) oauth2
 		}
 		return ts
 	}
-	jsonKey, err := ioutil.ReadFile(key)
+	conf, err := jwtConfigFromFile(key, scopes)
 	if err != nil {
-		log.Fatalf("Cannot read the JSON key file, err: %v", err)
-	}
-	conf, err := google.JWTConfigFromJSON(jsonKey, scopes...)
-	if err != nil {
-		log.Fatalf("google.JWTConfigFromJSON: %v", err)
+		log.Fatal(err)
 	}
 	return conf.TokenSource(ctx)
 }
+
+// JWTConfig reads the JSON private key file whose name is in the default
+// environment variable, and returns the jwt.Config it contains. It ignores
+// scopes.
+// If the environment variable is empty, it returns (nil, nil).
+func JWTConfig() (*jwt.Config, error) {
+	return jwtConfigFromFile(os.Getenv(envPrivateKey), nil)
+}
+
+// jwtConfigFromFile reads the given JSON private key file, and returns the
+// jwt.Config it contains.
+// If the filename is empty, it returns (nil, nil).
+func jwtConfigFromFile(filename string, scopes []string) (*jwt.Config, error) {
+	if filename == "" {
+		return nil, nil
+	}
+	jsonKey, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, fmt.Errorf("Cannot read the JSON key file, err: %v", err)
+	}
+	conf, err := google.JWTConfigFromJSON(jsonKey, scopes...)
+	if err != nil {
+		return nil, fmt.Errorf("google.JWTConfigFromJSON: %v", err)
+	}
+	return conf, nil
+}