minor symfony#18430 [FrameworkBundle] fixes grammar in container:debug command manual. (hhamon)

This PR was merged into the 2.3 branch.

Discussion
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[FrameworkBundle] fixes grammar in container:debug command manual.

| Q             | A
| ------------- | ---
| Branch?       | 2.3
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

Commits
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c3c092d [FrameworkBundle] fixes grammar in container:debug command manual.

Author: nicolas-grekas

src/Symfony/Bundle/FrameworkBundle/Command/ContainerDebugCommand.php

@@ -75,7 +75,7 @@ protected function configure()
 
   <info>php %command.full_name% --parameters</info>
 
-Display a specific parameter by specifying his name with the <info>--parameter</info> option:
+Display a specific parameter by specifying its name with the <info>--parameter</info> option:
 
   <info>php %command.full_name% --parameter=kernel.debug</info>
 EOF