followArtistsOrUsers method
Follows a list of users or artists.
type must be either 'artist' or 'user'.
Implementation
Future<void> followArtistsOrUsers(List<String> ids, String type) async {
assert(type == 'artist' || type == 'user', 'Type must be "artist" or "user"');
final uri = Uri.https(_baseApiHost, '/v1/me/following', {'type': type});
final body = {'ids': ids};
await _putJson(uri, body);
}