minor #13538 Fix documentation for a controllers with __invoke function in php routing (Ferror)

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

Discussion
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Fix documentation for a controllers with __invoke function in php routing

Hi, the current docs tell that proper using controller with ```__invoke``` class should be implemented by:
```
// if the action is implemented as the __invoke() method of the
// controller class, you can skip the ', method_name]' part:
// ->controller([BlogController::class])
```

which is wrong. The implementation should be without ```[]``` brackets:
```
// ->controller(BlogController::class)
```

Commits
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bcb84de Fix documentation for a controllers with __invoke function in php routing

Author: javiereguiluz

routing.rst

@@ -137,7 +137,7 @@ the ``BlogController``:
 
                 // if the action is implemented as the __invoke() method of the
                 // controller class, you can skip the ', method_name]' part:
-                // ->controller([BlogController::class])
+                // ->controller(BlogController::class)
             ;
         };