Fix another typo

README.md

@@ -109,7 +109,7 @@ User.find_each(&:save)
 ### `:allow_nil`
 
 You can pass `allow_nil: true` to the `friendly.find()` method if you want to
-avoid raising `ActiveRecord::RecordNotFound` and accept a `nil`.
+avoid raising `ActiveRecord::RecordNotFound` and accept `nil`.
 
 #### Example