chore(server): redirect if router.base specified in development

[atinux]

Types of changes

DX improvement.

Description

When we specify router.base:

// nuxt.config.js
export default {
  router: {
    base: '/hello/'
  }
}

When running nuxt dev, accessing http://localhost:3000 will display: Cannot GET /

With this PR, it will redirect to http://localhost:3000/hello/ and log to the console:

Checklist:

• I have added tests to cover my changes (if not applicable, please state why)
• All new and existing tests are passing.

[pi0]