Update dependency @google-cloud/trace-agent to v3

Author: renovate[bot]

trace/package.json

@@ -19,7 +19,7 @@
     "e2e-test": "repo-tools test deploy"
   },
   "dependencies": {
-    "@google-cloud/trace-agent": "2.11.0",
+    "@google-cloud/trace-agent": "3.4.0",
     "express": "4.16.4",
     "got": "8.3.2"
   },