[v4] Select prop-type appearance warning

[mshwery]

Select isn't listed as having any breaking changes in v4 but I'm getting prop-type warnings for not defining an appearance prop:

Warning: Failed prop type: Select: prop type `appearance` is invalid; it must be a function, usually from the `prop-types` package, but received `undefined`.

[jeroenransijn]

https://github.com/segmentio/evergreen/releases/tag/v4.0.0-2