minor symfony#8834 Changed symfony/web-server-bundle to dev package (xyNNN)

This PR was submitted for the master branch but it was merged into the 4.0 branch instead (closes symfony#8834).

Discussion
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Changed symfony/web-server-bundle to dev package

The symfony/web-server-bundle package should be installed as dev requirement. This bundle is not needable for production.

Commits
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72d2edb Changed symfony/web-server-bundle to dev package

Author: xabbuh

setup.rst

@@ -50,7 +50,7 @@ First, move into your new project and install the server:
 .. code-block:: terminal
 
     cd my-project
-    composer require server
+    composer require server --dev
 
 To start the server, run: