Convert server.js to module.exports (vercel#35181)

If different contexts (using Jest, using Nx, etc), server.js is getting imported when using middleware and throwing the error: "SyntaxError: Unexpected token 'export'".

fixes vercel#32848



## Bug

- [x] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`


Co-authored-by: JJ Kasper <[email protected]>

packages/next/server.js

@@ -1,2 +1,6 @@
-export { NextRequest } from 'next/dist/server/web/spec-extension/request'
-export { NextResponse } from 'next/dist/server/web/spec-extension/response'
+module.exports = {
+  NextRequest: require('next/dist/server/web/spec-extension/request')
+    .NextRequest,
+  NextResponse: require('next/dist/server/web/spec-extension/response')
+    .NextResponse,
+}