Can't run `cargo test --all` for `error-chain` anymore. The tests don't
compile because of `#[deny(invalid_doc_attributes)]`. Here's the error
message:
```
error: this attribute can only be applied at the crate level
--> tests/tests.rs:508:7
|
508 | #[doc(test)]
| ^^^^
|
= note: read <https://doc.rust-lang.org/nightly/rustdoc/the-doc-attribute.html#at-the-crate-level> for more information
= note: `#[deny(invalid_doc_attributes)]` on by default
help: to apply to the crate, use an inner attribute
|
508 | #![doc(test)]
| +
```
