docs: fix wrong header memcachedhandler in session

Author: ddevsr

user_guide_src/source/libraries/sessions.rst

@@ -671,7 +671,7 @@ deleted after Y seconds have passed (but not necessarily that it won't
 expire earlier than that time). This happens very rarely, but should be
 considered as it may result in loss of sessions.
 
-Configure RedisHandler
+Configure MemcachedHandler
 ----------------------
 
 The ``$savePath`` format is fairly straightforward here,