Travis config warnings

[rcowsill]

This is a very minor issue, but the travis dashboard lists some warnings for the config file:

root: deprecated key sudo (The key `sudo` has no effect anymore.)
cache: unknown key override ([npm ci, npm run cy ...])
root: missing dist, using the default xenial
root: missing os, using the default linux

I have a commit ready for PR that removes the unknown/deprecated lines and adds the missing ones.

[ckarande]

@rcowsill Thanks..Also notices your message on Gitter regarding Github Actions. In case this is still relevant, please make a PR.

[rcowsill]

@ckarande I submitted a PR as the change was ready to go. That said, it's not essential if the project is switched over to GitHub Actions CI. Feel free to close this issue and PR #223 in that case.