#[allow(...)] completions need closing parenthesis and brace

rls is unable to complete linter `allow` hints without a closing parenthesis and brace, but is able to complete them otherwise.

i.e. this works:

```rust
#[allow(̲̯ )]
```

but this doesn`t

```rust
#[allow(̲̯ 
```

(In case it's not rendered correctly, the completion is triggered at the same location immediately after the opening `(` in both samples.)