Incorrect function declaration for methods

[ramya-rao-a]

From microsoft/vscode-go#634 by @heliorosa

For the following program, the declaration for bigAdd is shown as bigAdd func(x, y *Int) *Int instead of bigAdd func(z, x, y *Int) *Int.

package main

import (
	"fmt"
	"math/big"
)

func main() {
	bigAdd := (*big.Int).Add
	a := big.NewInt(1)
	b := big.NewInt(2)
	c := bigAdd(new(big.Int), a, b)
	fmt.Println(a)
	fmt.Println(b)
	fmt.Println(c)
}