minor symfony#9069 Remove leading slash from rm -rf /vendor/* (ecodrutz)

This PR was merged into the 4.0 branch.

Discussion
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Remove leading slash from rm -rf /vendor/*

The leading slash makes the command delete the folder vendor from / of the file system instead the vendor folder from the current folder, which can cause major loss if someone has something there.

Commits
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53ffc4f Remove leading slash from rm -rf /vendor/*

Author: javiereguiluz

setup/flex.rst

@@ -195,7 +195,7 @@ manual steps:
 
    .. code-block:: terminal
 
-       $ rm -fr /vendor/*
+       $ rm -fr vendor/*
        $ composer install
 
 #. No matter which of the previous steps you followed. At this point, you'll have