Checking if the sent token is nil.

only bothers us on the first launch of the AppBlade SDK when we've already sent a permissions call.
updating sdkVersion to 0.5.1
Confirming new behavior is correct.

If the sent device secret is ever null when authenticating, treat it as an invalid request.
Merge pull request #81 from AppBlade/AT_null_check_of_device_secret

Null check of device secret