use `ignoreRestSiblings` for `no-unused vars` in eslint

[chrisdrackett]

this would be much nicer than using _unused or a eslint ignore comment when it comes to spreading objects to pull out variables.

[gaearon]

Oh, it's supported now? Is it a new feature?

[chrisdrackett]

<3 http://eslint.org/docs/rules/no-unused-vars#ignorerestsiblings

[gaearon]

Neat, want to send a PR?