google: change the snake case endpoint to kebab-case

See b/524330105 and go/mds-universe-domain-underscore

Change-Id: I378c2896b8ac3f01bd63dc9a0e34bd185aaf99ed
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/791160
Reviewed-by: Cody Oss <codyoss@google.com>
Commit-Queue: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Chris Smith <chrisdsmith@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
diff --git a/google/default.go b/google/default.go
index 6e57206..069f1aa 100644
--- a/google/default.go
+++ b/google/default.go
@@ -253,7 +253,7 @@
 	if metadata.OnGCE() {
 		id, _ := metadata.ProjectID()
 		universeDomainProvider := func() (string, error) {
-			universeDomain, err := metadata.Get("universe/universe_domain")
+			universeDomain, err := metadata.Get("universe/universe-domain")
 			if err != nil {
 				if _, ok := err.(metadata.NotDefinedError); ok {
 					// http.StatusNotFound (404)
diff --git a/google/default_test.go b/google/default_test.go
index 8b64058..17e8570 100644
--- a/google/default_test.go
+++ b/google/default_test.go
@@ -256,7 +256,7 @@
 }
 
 func TestComputeUniverseDomain(t *testing.T) {
-	universeDomainPath := "/computeMetadata/v1/universe/universe_domain"
+	universeDomainPath := "/computeMetadata/v1/universe/universe-domain"
 	universeDomainResponseBody := "example.com"
 	var requests int
 	s := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -277,7 +277,7 @@
 		Scopes: []string{scope},
 	}
 	universeDomainProvider := func() (string, error) {
-		universeDomain, err := metadata.Get("universe/universe_domain")
+		universeDomain, err := metadata.Get("universe/universe-domain")
 		if err != nil {
 			return "", err
 		}