doc: update Go1 release notes to use correct WalkFunc error signature.

filepath's WalkFunc handler now uses errors package, and not
os.Error

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5696067

doc/go1.html

@@ -1604,7 +1604,7 @@ instead of a <code>Visitor</code> interface value.
 </p>
 
 <pre>
-    type WalkFunc func(path string, info *os.FileInfo, err os.Error) os.Error
+    type WalkFunc func(path string, info os.FileInfo, err error) error
 </pre>
 
 <p>

doc/go1.tmpl

@@ -1503,7 +1503,7 @@ instead of a <code>Visitor</code> interface value.
 </p>
 
 <pre>
-    type WalkFunc func(path string, info *os.FileInfo, err os.Error) os.Error
+    type WalkFunc func(path string, info os.FileInfo, err error) error
 </pre>
 
 <p>