Declarative Macros 2.0 and Source Corruption

Declarative macros 2.0 were landed recently (https://github.com/rust-lang/rust/pull/40847), and I want to try them. The problem is that rustfmt corrupts the source. Consider this simple example:
```rust
pub macro reg() {}
```
Rustfmt converts it to:
```rust
pubmacro reg() {}
```
Which makes it uncompilable. Version of rustfmt: `0.2.5-nightly`.