Merge pull request rust-lang#2444 from smanilov/patch-22

Trivial: dedup word

Author: tshepang

src/doc/rustc-dev-guide/src/coroutine-closures.md

@@ -102,7 +102,7 @@ See the "follow-up: when do..." section below for an elaborated answer. The full
 
 When async closures are called with `AsyncFn`/`AsyncFnMut`, they return a coroutine that borrows from the closure. However, when they are called via `AsyncFnOnce`, we consume that closure, and cannot return a coroutine that borrows from data that is now dropped.
 
-To work around around this limitation, we synthesize a separate by-move MIR body for calling `AsyncFnOnce::call_once` on a coroutine-closure that can be called by-ref.
+To work around this limitation, we synthesize a separate by-move MIR body for calling `AsyncFnOnce::call_once` on a coroutine-closure that can be called by-ref.
 
 This body operates identically to the "normal" coroutine returned from calling the coroutine-closure, except for the fact that it has a different set of upvars, since we must *move* the captures from the parent coroutine-closure into the child coroutine.