docs: fix method name

Author: kenjis

user_guide_src/source/helpers/security_helper.rst

@@ -27,7 +27,7 @@ The following functions are available:
 
     Provides protection against directory traversal.
 
-    This function is an alias for ``\CodeIgniter\Security::sanitize_filename()``.
+    This function is an alias for ``\CodeIgniter\Security::sanitizeFilename()``.
     For more info, please see the :doc:`Security Library <../libraries/security>`
     documentation.