Suggested fix for macro typos adds extra exclamation point

```rust
fn main() {
    panec!()
}
```

RLS suggests a fix  ```you could try the macro: `panic!` ```.

When applying this fix, I get
```rust
fn main() {
    panic!!()
}
```

I observed this defect on
```
rls-preview 0.124.0-nightly (299a6a9 2017-12-25)
rust-lang-nursery/rls-vscode 0.3.2
```