Unable to parse `unsafe async fn`

I am running into a reproducible bug with ra that says `Syntax Error: expected existential, fn, trait or impl` right in between the `async` and `unsafe`. Running the check manually via `cargo` seems to report no errors.

```rust
struct Foo;

impl Foo {
	pub async unsafe fn bar() {}
}
```

should reproduce it.

Reference sha `d92a15c1637860a669970142abe37d1daf5f2c73`