www.responseHeaders is null when in airplane-mode

[Whyser]

simple-firebase-unity/SimpleFirebaseUnity/Firebase.cs

Line 797 in e0ea5d1

if (www.responseHeaders.ContainsKey("STATUS"))

Hey, as you can see in the title, it seems that www.responseHeaders is null when the user is in airplane-mode, not sure if this issue is specific to Unity 2017.2 (which we recently upgraded to), but we haven't experienced this before, that we know of (in Unity 5.5.0f3).

EDIT:
Seems to be related to Unity Bug: https://issuetracker.unity3d.com/issues/www-dot-responseheaders-object-is-null-if-there-is-no-internet-connection

[dkrprasetya]

Seems that the issue has been fixed in 2018.1.

I will put an additional checking there, in the next update.