Fix the svg file count

Author: Samuel Shifterovich

upgrade.md

@@ -68,7 +68,7 @@ Then, update any reference to the old directories in your `webpack.mix.js` file:
 
 A new directory, `svg`, was added to the `public` directory.
 
-It contains three svg files -- 403.svg, 404.svg, and 500.svg -- which are displayed on their respective error pages.
+It contains four svg files -- 403.svg, 404.svg, 500.svg, and 503.svg -- which are displayed on their respective error pages.
 
 You can get the files [from this commit](https://github.com/laravel/laravel/commit/0d43633f9f13de2c392331cdef3f1d48b04781ed).