message: src/lib.rs: Fix typo
diff: //!
  //! This crate is a microbenchmarking library which aims to provide strong
  //! statistical confidence in detecting and estimating the size of performance
  -//! improvements and regressions, whle also being easy to use.
  +//! improvements and regressions, while also being easy to use.
  //!
  //! See
  //! [the user guide](https://bheisler.github.io/criterion.rs/book/index.html)
  