minor #7410 Fix the command for validating the schema (celucatti)

This PR was submitted for the 2.8 branch but it was merged into the 2.7 branch instead (closes #7410).

Discussion
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Fix the command for validating the schema

It was basically the one for 3.1 and above in the page of the 2.8

Commits
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9b7335a Fix the command for validating the schema

Author: xabbuh

doctrine.rst

@@ -389,7 +389,7 @@ see the :ref:`doctrine-field-types` section.
 
     .. code-block:: terminal
 
-        $ php bin/console doctrine:schema:validate
+        $ php app/console doctrine:schema:validate
 
 .. _doctrine-generating-getters-and-setters: