API is not stable

[thanhbinh84]

It works well at first, then always throw errors:

I/flutter ( 4234): #0 Ipfinder.call (package:ipfinder/src/ipfinder.dart:89:7)
I/flutter ( 4234): #1 Ipfinder.authentication (package:ipfinder/src/ipfinder.dart:98:22)

With or without key didn't work

// Ipfinder ipFinder = Ipfinder(Env.ipFinderKey);
Ipfinder ipFinder = Ipfinder();
IpResponse auth = await ipFinder.authentication();