minor symfony#2372 [React] Fix broken Link in docs (xDeSwa)

This PR was squashed before being merged into the 2.x branch.

Discussion
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[React] Fix broken Link in docs

Fix broken Link

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Issues        | Fix
| License       | MIT

Commits
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ef14465 [React] Fix broken Link in docs

src/React/doc/index.rst

@@ -126,7 +126,7 @@ requires some extra steps.
 
 #. Compile your ``.jsx`` files to pure JavaScript files. This can be done by
    installing Babel and the ``@babel/preset-react`` preset. Example:
-   https://github.com/symfony/ux/blob/2.x/ux.symfony.com/package.json
+   https://github.com/symfony/ux/blob/2.x/ux.symfony.com/assets/react/build/package.json
 
 #. Point this library at the "built" controllers directory that contains the final
    JavaScript files: