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 glob@3.1.21: Glob versions prior to v9 are no longer supported
npm WARN deprecated rimraf@2.2.8: Rimraf versions prior to v4 are no longer supported
npm WARN deprecated minimatch@0.2.14: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated coffee-script@1.3.3: CoffeeScript on NPM has moved to "coffeescript" (no hyphen)
npm WARN deprecated graceful-fs@1.2.3: please upgrade to graceful-fs 4 for compatibility with current and future versions of Node.js
npm WARN deprecated glob@3.2.11: Glob versions prior to v9 are no longer supported
npm WARN deprecated minimatch@0.3.0: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated nomnom@1.8.1: Package no longer supported. Contact support@npmjs.com for more info.
npm notice created a lockfile as package-lock.json. You should commit this file.
npm WARN corpora@0.0.1 license should be a valid SPDX license expression

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