Spawn a child process.

@param  {string}    bin
the same as the 1st argument of `child_process.spawn()`.
@param  {Array}     args
the same as the 2nd argument of `child_process.spawn()`.
@param  {Object}    option
the same as the 3rd argument of `child_process.spawn()`.

@return {!PromiseLike<number>}
function spawnChildProcess(bin, args, option) {
    const result = spawnCancelableChild(bin, args, option);
    return result.process;
}