Documentation: mm: Fix typo in vm.txt

This patch fix a spelling typo in Documentation/sysctl/vm.txt
Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/sysctl/vm.txt

@@ -728,7 +728,7 @@ The default value is 60.
 
 - user_reserve_kbytes
 
-When overcommit_memory is set to 2, "never overommit" mode, reserve
+When overcommit_memory is set to 2, "never overcommit" mode, reserve
 min(3% of current process size, user_reserve_kbytes) of free memory.
 This is intended to prevent a user from starting a single memory hogging
 process, such that they cannot recover (kill the hog).