fix(deps): update dependency google-gax to ^0.20.0 (#138)

Author: renovate[bot]

packages/google-privacy-dlp/package.json

@@ -53,7 +53,7 @@
     "test": "npm run cover"
   },
   "dependencies": {
-    "google-gax": "^0.19.0",
+    "google-gax": "^0.20.0",
     "lodash.merge": "^4.6.0",
     "protobufjs": "^6.8.0"
   },