tools: lint for spacing around unary operators

tools: lint for spacing around unary operators

Enable `space-unary-ops` in `.eslintrc`. This prohibits things like:

    i ++        // use `i++` instead
    typeof(foo) // use `typeof foo` or `typeof (foo)` instead

Ref: https://github.com/nodejs/node/pull/4772#discussion_r51732299
PR-URL: https://github.com/nodejs/node/pull/5063
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: James M Snell <jasnell@gmail.com>