Support ESLint 3.9.0

This release covers all ESLint releases up to and including 3.9.0.

• New: no-useless-return set to warn (1).
• New: func-name-matching set to warn (1). This prevents a function foo from being assigned to a variable or property bar (with some special exceptions, e.g. module.exports = function foo () {}). This ought to be sensible but might have some false positives; will watch for that possibility.