Update gcloud versions (#359)

Update latest gcloud versions

Author: google-github-actions-bot

data/versions.json

@@ -492,5 +492,6 @@
   "535.0.0",
   "536.0.0",
   "536.0.1",
-  "537.0.0"
+  "537.0.0",
+  "538.0.0"
 ]