Cleaned up custom :menuRenderer example to use react-virtualized-select HOC

[bvaughn]

A live version of this PR can be seen here: http://bvaughn.github.io/react-select/

With PR #859 merged and v1.0.0-beta12 released, I released a new HOC- react-virtualized-select- so that I can take on the ownership of maintaining an interface between react-select and react-virtualized. A demo of the HOC can be seen here: http://bvaughn.github.io/react-virtualized-select/

This PR updates the example to use that HOC. (I think it's the simplest way to integrate the 2 libraries so it seems like the way we should show in a demo.)

[coveralls]

Coverage remained the same at 91.011% when pulling b85becf on bvaughn:master into 5c565b8 on JedWatson:master.

[coveralls]

Coverage remained the same at 91.011% when pulling 95367e7 on bvaughn:master into 5c565b8 on JedWatson:master.

[coveralls]

Coverage remained the same at 91.011% when pulling 1492b1e on bvaughn:master into 5c565b8 on JedWatson:master.

[omgaz]

LGTM, just update to the project contrib coding conventions specifically spacing. https://github.com/keystonejs/keystone/wiki/Coding-Standards

[bvaughn]

Hi @omgaz. I'm not sure I understand. Are you suggesting I change from tabs to spaces? I attempted to follow the default used in the other files.

[omgaz]

Hey, sorry my bad mis-read the contrib. Statement retracted! LGTM 🍥

[JedWatson]

Thanks @bvaughn! looks great.