doc/go1.5: correct archive/zip change

Change-Id: I7bac7b659b7ff425c6f896c286d0f89f05eff6bd
Reviewed-on: https://go-review.googlesource.com/7601Reviewed-by: Minux Ma <minux@golang.org>

doc/go1.5.txt

@@ -10,7 +10,7 @@ dragonfly/386 (https://golang.org/cl/7543)
 
 API additions and behavior changes:
 
-archive/zip: add WriterAt function (https://golang.org/cl/7445)
+archive/zip: add (*Writer).SetOffset method (https://golang.org/cl/7445)
 bufio: add Reader.Discard (https://golang.org/cl/2260)
 crypto/cipher: clarify what will happen if len(src) != len(dst) for the Stream interface. (https://golang.org/cl/1754)
 crypto/elliptic: add Name field to CurveParams struct (https://golang.org/cl/2133)