Minor edit to paragraph in Custom Events section (#610)

* Clarify and avoid using "In the event" to lead a phrase on events

* Update component-custom-events.md

src/guide/component-custom-events.md

@@ -33,7 +33,7 @@ app.component('custom-form', {
 })
 ```
 
-In the event a native event (e.g., `click`) is defined in the `emits` option, it will be overwritten by the event in the component instead of being treated as a native listener.
+When a native event (e.g., `click`) is defined in the `emits` option, the component event will be used __instead__ of a native event listener.
 
 ::: tip
 It is recommended to define all emitted events in order to better document how a component should work.