Update dependency @opencensus/core to ^0.0.18

Author: renovate-bot

opencensus/package.json

@@ -17,7 +17,7 @@
     "test": "repo-tools test run --cmd mocha -- system-test/*.test.js --timeout=5000 --exit"
   },
   "dependencies": {
-    "@opencensus/core": "^0.0.17",
+    "@opencensus/core": "^0.0.18",
     "@opencensus/exporter-stackdriver": "^0.0.17"
   },
   "devDependencies": {