feature suggestion: set trackBy default from label props

[castrix]

first of all, thank you for the component library, I just use the library today and I was confused when I tried to add searchable="true" props. Then I trace the problem with reading the source code, turns out that I didn't set the trackBy props because I use custom key object. I managed to resolve the problem, my suggestion is to force search by label prop if it's not empty

// useOptions.js
// line 419
return normalize(option[label.vaue || trackBy.value], strict.value).indexOf(normalize(search.value, strict.value)) !== -1

[adamberecz]

Thanks for the idea @castrix - added this in 2.3.0.