Declare encoding as utf-8 in pb2 files (via synth). (#8367)

Author: yoshi-automation

google/cloud/texttospeech_v1/proto/cloud_tts_pb2.py

@@ -1,19 +1,19 @@
 {
- "updateTime": "2019-06-14T12:34:21.212108Z",
+ "updateTime": "2019-06-15T12:32:48.504751Z",
  "sources": [
  {
  "generator": {
  "name": "artman",
- "version": "0.25.0",
- "dockerImage": "googleapis/artman@sha256:ef1a98ab1e2b8f05f4d9a56f27d63347aefe14020e5f2d585172b14ca76f1d90"
+ "version": "0.26.0",
+ "dockerImage": "googleapis/artman@sha256:6db0735b0d3beec5b887153a2a7c7411fc7bb53f73f6f389a822096bd14a3a15"
  }
  },
  {
  "git": {
  "name": "googleapis",
  "remote": "https://github.com/googleapis/googleapis.git",
- "sha": "c23b68eecb00c4d285a730a49b1d7d943cd56183",
- "internalRef": "253113405"
+ "sha": "7b58b37559f6a5337c4c564518e9573d742df225",
+ "internalRef": "253322136"
  }
  },
  {