fix pidfilepath typo

Author: David James

source/administration/configuration.txt

@@ -271,7 +271,7 @@ instance, but consider the following configuration values:
 .. code-block:: cfg
 
    dbpath = /srv/mongodb/db0/
-   pidfileath = /srv/mongodb/db0.pid
+   pidfilepath = /srv/mongodb/db0.pid
 
 The :setting:`dbpath` value controls the location of the
 :program:`mongod` instance's data directory. Ensure that each database