[chore] Update function lock file and modify travis to use yarn for f…

Merge pull request #2 from seblucas/dependabot/npm_and_yarn/handlebar…

[chore] update firebase to latest version should fix security alert

See https://github.com/facebook/jest/issues/8069
Also use pure-lockfile to be sure to always keep the good deps

[feat] Add another function to get the time of the most recent data

[fix] The context is needed in mutation

[fix] Try to fix breakage on function deploy

[feat] Remove pushError method not useful for now

[chore] Update package version

[chore] Updated firebase from 4.13.1 to 5.0.4