### What it does
Checks for `#[cfg_attr(rustfmt, rustfmt_skip)]` and suggests to replace it
with `#[rustfmt::skip]`.

### Why is this bad?
Since tool_attributes ([rust-lang/rust#44690](https://github.com/rust-lang/rust/issues/44690))
are stable now, they should be used instead of the old `cfg_attr(rustfmt)` attributes.

### Known problems
This lint doesn't detect crate level inner attributes, because they get
processed before the PreExpansionPass lints get executed. See
[#3123](https://github.com/rust-lang/rust-clippy/pull/3123#issuecomment-422321765)

### Example
```
#[cfg_attr(rustfmt, rustfmt_skip)]
fn main() { }
```

Use instead:
```
#[rustfmt::skip]
fn main() { }
```