Fix typo in render-function-api.md (#1076)

Author: mrts

src/guide/migration/render-function-api.md

@@ -11,7 +11,7 @@ This change will not affect `<template>` users.
 
 Here is a quick summary of what has changed:
 
-- `h` is now globally imported instead of passed to render functions as an arguments
+- `h` is now globally imported instead of passed to render functions as an argument
 - render function arguments changed to be more consistent between stateful and functional components
 - VNodes now have a flat props structure