`string` is not assignable to string union for TSX component props

Sample code : 

``` ts
type Foo = "f"|"o";
const FooComp = (props:{foo:Foo}) => <span>{props.foo}</span>;
<FooComp foo={"f"}/>; // Okay
<FooComp foo="f"/>; // Error : Type string is not assignable to "f"|"o";  Should be allowed and type checked 🌹
```

PS: can we get a JSX / TSX label. Would help me to search :rose: 
