Fix UA string

ts/util/getUserAgent.ts

@@ -1,6 +1,8 @@
 // Copyright 2020 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
+import os from 'os';
+
 import { getOwn } from './getOwn';
 
 const PLATFORM_STRINGS: { [platform: string]: string } = {
@@ -9,12 +11,19 @@ const PLATFORM_STRINGS: { [platform: string]: string } = {
   linux: 'Linux',
 };
 
-export function getUserAgent(appVersion: string): string {
+export function getUserAgent(
+  appVersion: string,
+  release = os.release()
+): string {
   // `process.platform` could be missing if someone figures out how to compile Signal on
   //   an unsupported OS and forgets to update this file. We'd rather send nothing than
   //   crash.
   const platformString = getOwn(PLATFORM_STRINGS, process.platform);
-  const platformStringWithSpace = platformString ? ` ${platformString}` : '';
 
-  return `Signal-Desktop/${appVersion}${platformStringWithSpace}`;
+  let result = `Signal-Desktop/${appVersion}`;
+  if (platformString) {
+    result += ` ${platformString} ${release}`;
+  }
+
+  return result;
 }