net/url: fix Encode doc comment

Encoded query strings are always sorted by key; the example wasn't.

R=golang-dev, dsymonds, minux.ma, bradfitz
CC=golang-dev
https://golang.org/cl/16430043

src/pkg/net/url/url.go

@@ -558,8 +558,8 @@ func parseQuery(m Values, query string) (err error) {
 	return err
 }
 
-// Encode encodes the values into ``URL encoded'' form.
-// e.g. "foo=bar&bar=baz"
+// Encode encodes the values into ``URL encoded'' form
+// ("bar=baz&foo=quux") sorted by key.
 func (v Values) Encode() string {
 	if v == nil {
 		return ""