Change to registerMediaConversions (#1544)

I think `registerModelConversions` should be `registerMediaConversions`. At least I couldn't find `registerModelConversions` anywhere.

docs/api/defining-conversions.md

@@ -3,7 +3,7 @@ title: Defining conversions
 weight: 2
 ---
 
-A media conversion can be added to your model in the `registerModelConversions`-function. It should start with a call to `addMediaConversion`. From there on you can use any of the methods available in the API. They are all chainable.
+A media conversion can be added to your model in the `registerMediaConversions`-function. It should start with a call to `addMediaConversion`. From there on you can use any of the methods available in the API. They are all chainable.
 
 Take a look in the [Defining conversions section](/laravel-medialibrary/v7/converting-images/defining-conversions/)
 for more details.