Replace `iota` variable in constant

[moeshin]

Fix #41

package test_tygo

const (
    A1 = -1
    A2 = iota
    A3
)

const (
    B1 = 1 + iota
    B2
    B3
)

const (
    C1 = -iota%2*2 + 1
    C2
    C3
)

// Code generated by tygo. DO NOT EDIT.

//////////
// source: type.go

export const A1 = -1;
export const A2 = 1;
export const A3 = 2;
export const B1 = 1 + 0;
export const B2 = 1 + 1;
export const B3 = 1 + 2;
export const C1 = -0 % 2 * 2 + 1;
export const C2 = -1 % 2 * 2 + 1;
export const C3 = -2 % 2 * 2 + 1;