**TypeScript Version:** nightly (2.1.0-dev.201xxxxx) When I add a decorator to a .js file, I no longer get the `'types' can only be used in a .ts file` error. Is this expected behavior? **Code** ``` js @SomeDecorator class SomeClass { foo(x:number) { } } ``` **Expected behavior:** `'types' can only be used in a .ts file` **Actual behavior:** no errors