flowControl.maxMessages is seemingly being ignored. I've created a small focused test repo to highlight the issue.

Environment details

• OS: Mac OSX
• Node.js version: 8.16.2
• npm version: 6.4.1
• @google-cloud/pubsub version: 1.1.2

Steps to reproduce

See: https://github.com/sjb933/gcloud-pubsub-maxMessage-bug

1. Clone project
2. npm install
3. Open test.ts and populate GOOGLE_PROJECT_ID with a proper project ID which you have authenticated access to
4. Execute the test with npm start
5. Observe the output

Observations:

Expected: 10 messages published, only 2 process concurrently.

Actual: 10 messages published, all 10 process concurrently.