Typo fix.

Fixed a minor typo in the 'Implementation Details' section of the comments.

Author: data-pup

src/lib.rs

@@ -86,7 +86,7 @@ fn main() {
 
 # Implementation details
 
-The `Deref` implementation uses a hidden static variable that is guarded by a atomic check on each access.
+The `Deref` implementation uses a hidden static variable that is guarded by an atomic check on each access.
 
 # Cargo features