build: fix Travis non-PR builds
Don't return non-zero if $TRAVIS_PULL_REQUEST
== "false".
Refs: https://github.com/nodejs/node/pull/24076#issuecomment-435716318
Checklist
-
commit message follows commit guidelines
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Don't return non-zero if $TRAVIS_PULL_REQUEST
== "false".
Refs: https://github.com/nodejs/node/pull/24076#issuecomment-435716318