minor #4617 [Filesystem] filesystem headlines match method names (xab…

…buh)

This PR was merged into the 2.3 branch.

Discussion
----------

[Filesystem] filesystem headlines match method names

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #4450

Commits
-------

9d77a6d filesystem headlines match method names

components/filesystem.rst

@@ -47,7 +47,7 @@ endpoint for filesystem operations::
     string, an array or any object implementing :phpclass:`Traversable` as
     the target argument.
 
-Mkdir
+mkdir
 ~~~~~
 
 :method:`Symfony\\Component\\Filesystem\\Filesystem::mkdir` creates a directory.
@@ -61,7 +61,7 @@ On posix filesystems, directories are created with a default mode value
     You can pass an array or any :phpclass:`Traversable` object as the first
     argument.
 
-Exists
+exists
 ~~~~~~
 
 :method:`Symfony\\Component\\Filesystem\\Filesystem::exists` checks for the
@@ -78,7 +78,7 @@ presence of all files or directories and returns ``false`` if a file is missing:
     You can pass an array or any :phpclass:`Traversable` object as the first
     argument.
 
-Copy
+copy
 ~~~~
 
 :method:`Symfony\\Component\\Filesystem\\Filesystem::copy` is used to copy
@@ -92,7 +92,7 @@ the third boolean argument::
     // image.jpg will be overridden
     $fs->copy('image-ICC.jpg', 'image.jpg', true);
 
-Touch
+touch
 ~~~~~
 
 :method:`Symfony\\Component\\Filesystem\\Filesystem::touch` sets access and
@@ -111,7 +111,7 @@ your own with the second argument. The third argument is the access time::
     You can pass an array or any :phpclass:`Traversable` object as the first
     argument.
 
-Chown
+chown
 ~~~~~
 
 :method:`Symfony\\Component\\Filesystem\\Filesystem::chown` is used to change
@@ -127,7 +127,7 @@ the owner of a file. The third argument is a boolean recursive option::
     You can pass an array or any :phpclass:`Traversable` object as the first
     argument.
 
-Chgrp
+chgrp
 ~~~~~
 
 :method:`Symfony\\Component\\Filesystem\\Filesystem::chgrp` is used to change
@@ -143,7 +143,7 @@ the group of a file. The third argument is a boolean recursive option::
     You can pass an array or any :phpclass:`Traversable` object as the first
     argument.
 
-Chmod
+chmod
 ~~~~~
 
 :method:`Symfony\\Component\\Filesystem\\Filesystem::chmod` is used to change
@@ -159,7 +159,7 @@ the mode of a file. The fourth argument is a boolean recursive option::
     You can pass an array or any :phpclass:`Traversable` object as the first
     argument.
 
-Remove
+remove
 ~~~~~~
 
 :method:`Symfony\\Component\\Filesystem\\Filesystem::remove` is used to remove
@@ -172,7 +172,7 @@ files, symlinks, directories easily::
     You can pass an array or any :phpclass:`Traversable` object as the first
     argument.
 
-Rename
+rename
 ~~~~~~
 
 :method:`Symfony\\Component\\Filesystem\\Filesystem::rename` is used to rename