minor #16462 Update some code (IamBeginnerC)

This PR was submitted for the 6.0 branch but it was merged into the 4.4 branch instead.

Discussion
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Update some code

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Commits
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a20ace6 Update some code

Author: javiereguiluz

configuration/override_dir_structure.rst

@@ -51,7 +51,7 @@ method in the ``Kernel`` class of your application::
     {
         // ...
 
-        public function getCacheDir()
+        public function getCacheDir() : string
         {
             return dirname(__DIR__).'/var/'.$this->environment.'/cache';
         }
@@ -84,7 +84,7 @@ method::
     {
         // ...
 
-        public function getLogDir()
+        public function getLogDir() : string
         {
             return dirname(__DIR__).'/var/'.$this->environment.'/log';
         }