currency: fix format in example

Fixes golang/go#23233

Change-Id: Ie89140502cc966acedea4abbaf66214b90ce570a
Reviewed-on: https://go-review.googlesource.com/85398
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

currency/example_test.go

diff --git a/currency/example_test.go b/currency/example_test.go
index f7984aa..519c872 100644
--- a/currency/example_test.go
+++ b/currency/example_test.go
@@ -16,12 +16,12 @@
 	for it := currency.Query(currency.Date(t1799)); it.Next(); {
 		from := ""
 		if t, ok := it.From(); ok {
-			from = t.Format("2006-01-01")
+			from = t.Format("2006-01-02")
 		}
 		fmt.Printf("%v is used in %v since: %v\n", it.Unit(), it.Region(), from)
 	}
 	// Output:
-	// GBP is used in GB since: 1694-07-07
+	// GBP is used in GB since: 1694-07-27
 	// GIP is used in GI since: 1713-01-01
 	// USD is used in US since: 1792-01-01
 }