minor #11451 Update psr4_class_loader.rst to fix incorrect path in directory structure (siva-epari)

This PR was merged into the 3.4 branch.

Discussion
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Update psr4_class_loader.rst to fix incorrect path in directory structure

Incorrect path shown in directory structure. demo.php refers to /lib/ but directory structure asks to add downloaded components to /libs/

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Commits
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ae0fc1e Update psr4_class_loader.rst

Author: javiereguiluz

components/class_loader/psr4_class_loader.rst

@@ -27,7 +27,7 @@ The directory structure will look like this:
 
 .. code-block:: text
 
-    libs/
+    lib/
         ClassLoader/
             Psr4ClassLoader.php
             ...