Update GitHub Actions and remove redundant Travis CI

[hugovk]

Travis CI is long gone: https://app.travis-ci.com/github/dariusk/corpora/

There are some npm warnings about old versions and the licence, but these can wait for another time.

npm WARN deprecated [email protected]: Glob versions prior to v9 are no longer supported
npm WARN deprecated [email protected]: Rimraf versions prior to v4 are no longer supported
npm WARN deprecated [email protected]: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated [email protected]: CoffeeScript on NPM has moved to "coffeescript" (no hyphen)
npm WARN deprecated [email protected]: please upgrade to graceful-fs 4 for compatibility with current and future versions of Node.js
npm WARN deprecated [email protected]: Glob versions prior to v9 are no longer supported
npm WARN deprecated [email protected]: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated [email protected]: Package no longer supported. Contact [email protected] for more info.
npm notice created a lockfile as package-lock.json. You should commit this file.
npm WARN [email protected] license should be a valid SPDX license expression

https://github.com/hugovk/corpora/actions/runs/16990128894/job/48167295669#step:5:14