docs.rs build fails for 0.4.4

The docs.rs build for 0.4.4 failed ([logs](https://docs.rs/crate/mundane/0.4.4/builds/357678)). I believe this is caused by https://github.com/rust-lang/docs.rs/issues/1303.

Start with the docs.rs build logs for mundane 0.4.4 and review docs.rs issue 1303, which the report identifies as the likely cause. Determine whether the failure can be addressed in this repository; done means the 0.4.4 docs.rs build succeeds or the external dependency and required next step are clearly documented.

Written by the indexing model from the issue text.