Faster retries when a server cannot be reached

When a connection to the API is refused before your request leaves, the SDKs (JavaScript, Python, Go, Java and Ruby) send it again at once instead of after a quarter of a second, so a server that just went away costs your call almost nothing. A request that may have reached a server waits and retries under its idempotency key as before, so nothing runs twice. In each SDK's next release.