os/signal: fix wrong constant name in the documentation

os.SIGINT is not defined, os.Interrupt or syscall.SIGINT should be used.

Change-Id: I39867726d28e179d1160a4fd353b7bea676c9dbb
Reviewed-on: https://go-review.googlesource.com/23127
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: kostya-sh

src/os/signal/doc.go

@@ -205,8 +205,8 @@ before raising the signal.
 Windows
 
 On Windows a ^C (Control-C) or ^BREAK (Control-Break) normally cause
-the program to exit. If Notify is called for os.SIGINT, ^C or ^BREAK
-will cause os.SIGINT to be sent on the channel, and the program will
+the program to exit. If Notify is called for os.Interrupt, ^C or ^BREAK
+will cause os.Interrupt to be sent on the channel, and the program will
 not exit. If Reset is called, or Stop is called on all channels passed
 to Notify, then the default behavior will be restored.