Built app doesn't launch with Electron 6.0.0 due to outdated electron-builder

[caesar]

Describe the bug
Electron 6.0.0. has three new Helper apps which must be included in the build.
The version of electron-builder used by this module doesn't handle this.
A new version 21.2.0 was just released which correctly copies the new helpers.

To Reproduce

1. Set up a vue-cli-plugin-electron-builder with Electron 6.0.0.
2. Build.
3. Try launching the app.

Expected behavior
vue-cli-plugin-electron-builder should work with Electron 6.0.0

Environment (please complete the following information):

• OS and version: macOS (any)
• node version: any
• npm version: any
• yarn version (if used): any
• vue-cli-plugin-electron-builder version : 1.3.6
• electron version: 6.0.0

Additional context

• New helper apps on macOS in Electron v6 electron-userland/electron-builder#4104
• My app is crashing on start-up when packaged on Electron v6 electron/electron#19511

[nklayman]

Fixed in v1.4.0 by upgrading electron-builder version.