Fixed automaticallyIdentifyLanguages method on macOS to disable automatic language detection without calling switchLanguage again.

// Calling setDictionary on the macOS implementation of @nornagon/spellchecker
// is the only way to set the automaticallyIdentifyLanguages property on the
// native NSSpellchecker. Calling switchLanguage with a language will set it false,
// while calling it with an empty language will set it to true