Update validation.md (#264)

Small typo. 

OT: What a masterpiece these docs are. Thanks. This level is a new benchmark to aim for myself personally when doing documentation.

Author: bn-l

docs/guide/validation.md

@@ -32,7 +32,7 @@ Finally, since Inertia apps never generate `422` responses, Inertia needs anothe
 
 ## Sharing errors
 
-In order for your server-side validation errors to be available client-side, your server-side framework must share them via the `errors` prop. Inertia's Rails adapter do this automatically.
+In order for your server-side validation errors to be available client-side, your server-side framework must share them via the `errors` prop. Inertia's Rails adapter does this automatically.
 
 ## Displaying errors