fallbackLng does not support object type at i18next-http-middleware version 3.8.1 any more

## 🐛 Bug Report

fallbackLng does not support object type at i18next-http-middleware version 3.8.1 any more

## To Reproduce

1. We always set the fallbackLng with object as below(i18next-http-middleware version 3.8.0 ), it works.

```js
fallbackLng: {
default: ['en'],
},
```
2. But after we upgrade i18next-http-middleware version 3.8.1, it has errors as below:

TypeError: _this.fallbacks.map is not a function
at /i18next-http-middleware@3.8.1/node_modules/i18next-http-middleware/esm/LanguageDetector.js:93:70
at Array.forEach ()
at LanguageDetector.detect (i18next-http-middleware@3.8.1/node_modules/i18next-http-middleware/esm/LanguageDetector.js:77:22)
at i18nextMiddleware (i18next-http-middleware@3.8.1/node_modules/i18next-http-middleware/esm/index.js:79:47)
at Layer.handle [as handle_request] (/express@4.21.2/node_modules/express/lib/router/layer.js:95:5)

if we change below , it works

```js
fallbackLng: ['en'],
```

## Expected behavior

fallbackLng support the object type

Start at esm/LanguageDetector.js around line 93 and trace how LanguageDetector.detect processes fallbackLng. Reproduce the failure with the object form shown in the issue, then verify that fallbackLng supports both the object form and the existing array form without the map error.

Written by the indexing model from the issue text.