fix(deps): update dependency google/cloud-text-to-speech to v2 (GoogleCloudPlatform#2129)

Co-authored-by: Brent Shaffer <betterbrent@google.com>

Author: renovate-bot

texttospeech/composer.json

@@ -1,5 +1,5 @@
 {
     "require": {
-        "google/cloud-text-to-speech": "^1.8"
+        "google/cloud-text-to-speech": "^2.0"
     }
 }