time: fix Time.ZoneOffset documentation

R=rsc
CC=golang-dev
https://golang.org/cl/4240090

src/pkg/time/time.go

@@ -23,7 +23,7 @@ type Time struct {
 	Month, Day           int    // Jan-2 is 1, 2
 	Hour, Minute, Second int    // 15:04:05 is 15, 4, 5.
 	Weekday              int    // Sunday, Monday, ...
-	ZoneOffset           int    // seconds east of UTC, e.g. -7*60 for -0700
+	ZoneOffset           int    // seconds east of UTC, e.g. -7*60*60 for -0700
 	Zone                 string // e.g., "MST"
 }