build,tools: tweak the travis config

PR-URL: https://github.com/nodejs/node/pull/22417


Reviewed-By: George Adams <george.adams@uk.ibm.com>
Reviewed-By: Matheus Marchini <matheus@sthima.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>