Trial period check in Google Play doesn't work

[catacs]

When I try to call trial? method from CandyCheck::PlayStore::Subscription class i get false when a subscription is trial. Checking the google play documentation, the added a new payment_state with value 2 which is trial.

https://developers.google.com/android-publisher/api-ref/purchases/subscriptions

paymentState | integer | The payment state of the subscription. Possible values are:

0. Payment pending
1. Payment received
2. Free trial

[jnbt]

This is a good point, we should allow also the value 2

[jnbt]

@christophweegen Can you please have a look here. I think we need to whitelist the value 2 on CandyCheck::PlayStore::Subscription#trail?.