minor #9869 Use version number in installer command (weaverryan)

This PR was merged into the 3.4 branch.

Discussion
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Use version number in installer command

Force the installer to use 3.4 - otherwise the command doesn't work.

Commits
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2a4b0b4 Use version name in installer command

Author: javiereguiluz

setup.rst

@@ -59,7 +59,7 @@ with the ``new`` command:
 
 .. code-block:: terminal
 
-    $ symfony new my_project_name
+    $ symfony new my_project_name 3.4
 
 This command creates a new directory called ``my_project_name/`` that contains
 an empty project based on the most recent stable Symfony version available. In