Remove quotes around App\Entity namespace

Those quotes will appear in the generated entities namespace, thus causing a PHP ParseError.

Author: gsylvestre

doctrine/reverse_engineering.rst

@@ -56,7 +56,7 @@ table fields.
 
 .. code-block:: terminal
 
-    $ php bin/console doctrine:mapping:import 'App\Entity' annotation --path=src/Entity
+    $ php bin/console doctrine:mapping:import App\Entity annotation --path=src/Entity
 
 This command line tool asks Doctrine to introspect the database and generate
 new PHP classes with annotation metadata into ``src/Entity``. This generates two