documentation: fix erroneous email address.

Hey, at least it has both l's.
Reported-by: Marin Mitov <mitov@issp.bas.bg>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Documentation/cpu-hotplug.txt

@@ -2,7 +2,7 @@
 
 		Maintainers:
 		CPU Hotplug Core:
-			Rusty Russell <rusty@rustycorp.com.au>
+			Rusty Russell <rusty@rustcorp.com.au>
 			Srivatsa Vaddagiri <vatsa@in.ibm.com>
 		i386:
 			Zwane Mwaikambo <zwane@arm.linux.org.uk>