minor symfony#9412 Use create-project instead of require to create reproducer project (magnetik)

This PR was merged into the 4.0 branch.

Discussion
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Use create-project instead of require to create reproducer project

`composer require symfony/skeleton bug_app` is a syntax error (as `bug_app` is required to be a version constraint).

So I think this was a typo

Commits
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0fe4c71 Use create-project instead of require to create reproducer project

Author: javiereguiluz

contributing/code/reproducer.rst

@@ -39,7 +39,7 @@ a PHP script, it's better to reproduce the bug by creating a new project. To do
 
 .. code-block:: terminal
 
-    $ composer require symfony/skeleton bug_app
+    $ composer create-project symfony/skeleton bug_app
 
 2. Now you must add the minimum amount of code to reproduce the bug. This is the
    trickiest part and it's explained a bit more later.