encoding/hex: minor cleanup

Change-Id: I404fd946dd0607fa41e2abe0d1d8081d4433ff0a
Reviewed-on: https://go-review.googlesource.com/19762Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/encoding/hex/hex.go

@@ -105,7 +105,7 @@ func Dump(data []byte) string {
 	dumper := Dumper(&buf)
 	dumper.Write(data)
 	dumper.Close()
-	return string(buf.Bytes())
+	return buf.String()
 }
 
 // Dumper returns a WriteCloser that writes a hex dump of all written data to