Most likely your credentials are incorrect at the deployment time. If you encrypted your credentials, they were probably encrypted incorrectly. Try specifying the repo with -r, and the endpoint with --pro (for .com), or --org (for .org); e.g.,
travis encrypt -r OWNER/REPO --com
Alternatively, try setting it on the settings panel.
All configurations here looks correct. However, If you happened to be trying to deploy a web application built be webpack on Firebase Hosting you might want to try to set you cleanup option to persist the built artifact.