Update src/borrow_check/region_inference.md

Co-Authored-By: csmoe <csmoe@msn.com>

Author: mark-i-m

src/borrow_check/region_inference.md

@@ -129,7 +129,7 @@ the type of `foo`   the type `bar` expects
 ```
 
 We handle this sort of subtyping by taking the variables that are
-bound in the supertype and replace them with
+bound in the supertype and replacing them with
 [universally quantified](../appendix/background.html#quantified)
 representatives, written like `!1`. We call these regions "placeholder
 regions" – they represent, basically, "some unknown region".