time: fix 400 year offset in comment

Change-Id: I33c2c222ea884d9ff57800ea5185644b5d8e591a
Reviewed-on: https://go-review.googlesource.com/14034Reviewed-by: Minux Ma <minux@golang.org>

src/time/time.go

@@ -180,7 +180,7 @@ func (d Weekday) String() string { return days[d] }
 // everywhere.
 //
 // The calendar runs on an exact 400 year cycle: a 400-year calendar
-// printed for 1970-2469 will apply as well to 2470-2869.  Even the days
+// printed for 1970-2469 will apply as well to 2370-2769.  Even the days
 // of the week match up.  It simplifies the computations to choose the
 // cycle boundaries so that the exceptional years are always delayed as
 // long as possible.  That means choosing a year equal to 1 mod 400, so