minor #5145 Update introduction.rst (cafferata)

This PR was submitted for the 2.6 branch but it was merged into the 2.3 branch instead (closes #5145).

Discussion
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Update introduction.rst

Little PHP-CS-Fixer

Commits
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df700da Update introduction.rst

Author: wouterj

components/console/introduction.rst

@@ -85,7 +85,7 @@ an ``Application`` and adds commands to it::
     use Symfony\Component\Console\Application;
 
     $application = new Application();
-    $application->add(new GreetCommand);
+    $application->add(new GreetCommand());
     $application->run();
 
 Test the new console command by running the following