minor symfony#12580 Fix log directory parameter (merguezzz)

This PR was merged into the 4.3 branch.

Discussion
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Fix log directory parameter

kernel.logs_dir instead of kernel.log_dir

Commits
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c1d34a8 Correct log dir parameter

Author: OskarStark

reference/configuration/kernel.rst

@@ -125,7 +125,7 @@ This returns the absolute path of the log directory of your Symfony project.
 It's calculated automatically based on the current
 :ref:`environment <configuration-environments>`.
 
-This value is exposed via the ``kernel.log_dir`` configuration parameter and
+This value is exposed via the ``kernel.logs_dir`` configuration parameter and
 the :method:`Symfony\\Component\\HttpKernel\\Kernel::getLogDir` method. To
 change this setting, override the ``getLogDir()`` method to return the right
 log directory.