Update source/administration/journaling.txt

Fix the typo

Author: kosmakoff

source/administration/journaling.txt

@@ -213,7 +213,7 @@ write *many* bytes of data per-second, the journal directory should
 contain only two or three journal files.
 
 To limit the size of each journal file to 128 megabytes, use the
-:setting`smallfiles` run time option when starting :program:`mongod`.
+:setting:`smallfiles` run time option when starting :program:`mongod`.
 
 To speed the frequent sequential writes that occur to the current
 journal file, you can ensure that the journal directory is on a