minor #982 Add the missing quotes in the code in the section Configuration for the StimulusBundle (makraz)

This PR was merged into the 2.x branch.

Discussion
----------

Add the missing quotes in the code in the section Configuration for the StimulusBundle

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Tickets       | Fix #981
| License       | MIT

I added a missing quotes in the code in the section Configuration for the StimulusBundle.

Commits
-------

148e8f2 Add the missing quotes in the code in the section Configuration for the StimulusBundle

Author: kbond

src/StimulusBundle/doc/index.rst

@@ -342,7 +342,7 @@ directory and the ``controllers.json`` file if you need to use different paths:
     stimulus:
         # the default values
         controller_paths:
-            - %kernel.project_dir%/assets/controllers
+            - '%kernel.project_dir%/assets/controllers'
         controllers_json: '%kernel.project_dir%/assets/controllers.json'
 
 .. _manual-installation: