Templates that add to the plugins config array are broken in beta.68

[erickzhao]

Pre-flight checklist

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project uses.
• I have searched the issue tracker for a bug that matches the one I want to file, without success.

Electron Forge version

6.0.0-beta.68

Electron version

N/A

Operating system

All

Last known working Electron Forge version

6.0.0-beta.67

Expected behavior

When initializing a new Electron Forge app, I expect the plugins array to be properly configured.

{
  plugins: [{
    name: "@electron-forge/plugin-webpack",
    config: { /**...*/ }
}]

Actual behavior

We still have the old syntax present and it won't work with the latest beta of Forge.

{
  plugins: [[
    "@electron-forge/plugin-webpack",
    { /**...*/ }
  ]]
}

Steps to reproduce

yarn create electron-app --template=webpack

Or use electron-forge init directly.

Additional information

No response

[MarshallOfSound]

Fixed in #2990