Erro ao exportar módulo

Estou tomando esse erro ao exportar o módulo (interno) timer, to apanhando feio... =S

Alguma ideia de como solucionar esse problema?

Uncaught Error: Cannot find module './timer'
    at Module._resolveFilename (module.js:485:15)
    at Function.Module._resolveFilename (D:\workspace\pocs\electron-timer\node_modules\electron\dist\resources\electron.asar\common\reset-search-paths.js:35:12)
    at Function.Module._load (module.js:437:25)
    at Module.require (module.js:513:17)
    at require (internal/module.js:11:18)
    at file:///D:/workspace/pocs/electron-timer/app/js/render.js:2:15

timer.js

const moment = require('moment');
let  seconds;
let time;
let timer;

module.exports = {
    start: function(el){
        time = moment.duration(el.textContent);
        seconds = time.asSeconds();
        clearInterval(timer);
        timer = setInterval(() => {
            seconds++;
            el.textContent = this.formatTime(seconds);
        }, 1000);
        console.log("iniciou!");
    },
    stop: function(el){

    },
    formatTime: function(seconds){
        return moment().startOf('day').seconds(seconds).format("HH:mm:ss");
    }
}

render.js

const { ipcRenderer } = require('electron');
const timer = require('./timer');

let aboutLink = document.querySelector('#about-link');
let playButton = document.querySelector(".play-button");
let timeSpan = document.querySelector(".time-clock");


aboutLink.addEventListener('click', function(){
    ipcRenderer.send('open-about-window');
});

let images = ['img/play-button.svg', 'img/stop-button.svg'];
playButton.addEventListener('click', function(){
    images = images.reverse();
    timer.start(timeSpan);
    playButton.src = images[0];
});