minor #18291 [Frontend] Update package.json example path (mttsch)

This PR was submitted for the 6.2 branch but it was merged into the 5.4 branch instead.

Discussion
----------

[Frontend] Update package.json example path

See symfony/ux@561a4a3

Commits
-------

b7d5c25 [Frontend] Update package.json example path

Author: javiereguiluz

frontend/ux.rst

@@ -59,7 +59,7 @@ PHP package. For example:
     {
         "devDependencies": {
             "...": "",
-            "@symfony/ux-chartjs": "file:vendor/symfony/ux-chartjs/Resources/assets"
+            "@symfony/ux-chartjs": "file:vendor/symfony/ux-chartjs/assets"
         }
     }