memcg: update maintainer list

Nishimura-san have been working for memcg very good. His review and tests
give us much improvements and account migraiton which he is now
challenging is really important.

He is a stakeholder.

Signed-off-by: KAMEZAWA Hiroyuki <[e-mail]>
Cc: Daisuke Nishimura <[e-mail]>
Cc: Balbir Singh <[e-mail]>
Acked-by: Pavel Emelyanov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

MAINTAINERS

···
 
 MEMORY RESOURCE CONTROLLER
 M:	Balbir Singh <[e-mail]>
-M:	Pavel Emelyanov <[e-mail]>
+M:	Daisuke Nishimura <[e-mail]>
 M:	KAMEZAWA Hiroyuki <[e-mail]>
 L:	[e-mail]
 S:	Maintained