update typescript definition file

- Get latest from https://github.com/DefinitelyTyped/DefinitelyTyped/tree/master/types/i18next
- Set return type to `Promise` for `init`, `changeLanguage`, `loadNamespaces`, `loadLanguages` and `reloadResources` methods
- Remove `DetectionPluginOptions`, `BackendPluginOptions` and `CachePluginOptions` since simple `object` work in the same way
- Specify range of values for `compatibilityJSON`
- Add interfaces for modules: `backend`, `languageDetector`, 'postProcessor' and `logger`
- Uppercase first letter in comment