test: add GHA testing, nuke Travis

[msimerson]

Hello again. 👋🏻

• ci: replace travis (dead) with Github Actions GHA)
• ci: automatically test on ubuntu & windows
• ci: automatically test on the LTS versions of node.js
• ci: also test in node 10. Perhaps a min node.js version should be specified in package.json?
• deps: remove mocha & eslint, they get auto-installed by npx when needed
• included are working configs for coveralls and codecov, if you're so inclined
• update CI badge URL, remove broken badges

You can preview the test runs in image below and in the Actions tab of my fork

closes #220

[msimerson]