Fix crate documentation typo
//! encouraged to read it. The `async-std` source is generally high
//! quality and a peek behind the curtains is often enlightening.
//!
-//! Modules in this crate are organized in the same way as in `async-std`, except blocking
+//! Modules in this crate are organized in the same way as in `std`, except blocking
//! functions have been replaced with async functions and threads have been replaced with
//! lightweight tasks.
//!
