Typo in Documentation/scheduler/sched-stats.txt

I have found a very small typo in Documentation/scheduler/sched-stats.txt.
See the end of this mail.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>