tools: lint for empty character classes in regex

tools: lint for empty character classes in regex

Enable linting rule to forbid empty character classes in regular
expressions. See http://eslint.org/docs/rules/no-empty-character-class

Organize "Possible Error" rules in .eslintrc in alphabetical order to
match eslint documentation.

PR-URL: https://github.com/nodejs/node/pull/5115
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>