fix typo in tutorial/expire-data.txt

Author: jrassi

source/tutorial/expire-data.txt

@@ -32,7 +32,7 @@ in seconds to create an expiring collection. TTL collections set the
 :collflag:`usePowerOf2Sizes` collection flag, which means MongoDB must
 allocate more disk space relative to data size. This approach helps
 mitigate the possibility of storage fragmentation caused by frequent
-delete operations and leads to more predictable storage use patters.
+delete operations and leads to more predictable storage use patterns.
 
 Constraints
 -----------