Type Lookup 
by Anthony Fu @antfu
Sometimes, you may want to look up a type in a union by its attributes.
In this challenge, we would like to get the corresponding type by searching for the common `type` field in the union `Cat | Dog`. In other words, we will expect to get `Dog` for `LookUp` and `Cat` for `LookUp` in the following example.
```ts
interface Cat {
type: 'cat'
breeds: 'Abyssinian' | 'Shorthair' | 'Curl' | 'Bengal'
}
interface Dog {
type: 'dog'
breeds: 'Hound' | 'Brittany' | 'Bulldog' | 'Boxer'
color: 'brown' | 'white' | 'black'
}
type MyDogType = LookUp // expected to be `Dog`
```
