fix(deps): update dependency @google-cloud/pubsub to v3 (#543)

Author: renovate-bot

background/package.json

@@ -15,7 +15,7 @@
   },
   "dependencies": {
     "@google-cloud/firestore": "^5.0.0",
-    "@google-cloud/pubsub": "2.19.4",
+    "@google-cloud/pubsub": "3.0.1",
     "@google-cloud/storage": "^5.0.0",
     "express": "^4.16.4"
   },

background/server/package.json

@@ -11,7 +11,7 @@
   "license": "Apache-2.0",
   "dependencies": {
     "@google-cloud/firestore": "^5.0.0",
-    "@google-cloud/pubsub": "^2.0.0",
+    "@google-cloud/pubsub": "^3.0.0",
     "body-parser": "^1.19.0",
     "express": "^4.17.1",
     "handlebars": "^4.2.0",