jsx-no-lambda: allow lambdas on ref attribute

[testerez]

Fixes issue #26

The main performance drop with arrow function as prop is due to pure components re-rendering when it could be avoided. The creation of a new function is not a real problem.

The ref attribute is not part of the props so it's ok to use an arrow function here.

See: facebook/react#9086 (comment)

Rather than adding a configuration, I simply ignore "ref" attribute. I think that this is what makes the more sense in most situations.

[palantirtech]

Thanks for your interest in palantir/tslint-react, @testerez! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[adidahiya]

thanks @testerez