Add eslint integration

[miketaylr]

It would be nice if we used the same ruleset for this tool that we use for webcompat.com (minus globals):

https://github.com/webcompat/webcompat.com/blob/master/.eslintrc

[zoepage]

Agreed. Will happen before publishing.

ToDo's

• add ESLint
• add Travis Ci integration
• add tests (tap / tape)

(This can happen in parallel while webcompat/webcompat.com#1310 (comment))

[zoepage]

Eslint works perfectly. Two files got excluded on purpose, as they hold mostly special chars and no code logic.
👉 https://github.com/webcompat/webcompat-cli-tool/blob/master/lib/messages.js
👉 https://github.com/webcompat/webcompat-cli-tool/blob/master/lib/schema.js

Run npm run lint to run the linter.

Travis integration as well as the test will follow after we've done the refactor in webcompat/webcompat.com#1310 (comment)