Support ESLint 3.4.0

This release adds new rules found in ESLint v3.4.0, and also refines / removes some existing rules.

New Rules

• symbol-description: warn if Symbol description strings are omitted. Descriptions are helpful in debugging.
• class-methods-use-this: warn if ES6 class methods do not use this, in which case they can be made static.

Updated rules

• wrap-iife: added 'any' option to allow either pattern: (function () {}()) or (function () {})().
• global-require: turned off as there are valid reasons for selectively requiring modules.
• quote-props: changed from error to warn.