title: Application entry file does not exist in Electron Builder
body: <p>I have a minimal electron app and I am trying to build it (it runs fine). My package.json is</p>
  
  <pre><code>  "main": "main.js",
    "scripts": {
      "start": "electron -r babel-register .",
      "package": "build --dir",
      "postinstall": "electron-builder install-app-deps"
    },
    // dependencies
    "build": {
      "appId": "com.karmadust.mancuspianconvert",
      "files": [
        "node_modules/**/*"
      ],
      "directories": {
        "buildResources": "assets"
      }
    }
  </code></pre>
  
  <p>When I run <code>npm run package</code> I get:</p>
  
  <pre><code>Application entry file "main.js" in the "[path-to-project]/dist/mac/myapp.app/Contents/Resources/app.asar" does not exist. Seems like a wrong configuration.
  </code></pre>