GsonSubType removes subtype key from json

[LachlanMcKee]

The GsonSubType annotation uses a key to determine which object to create. Unfortunately this is removing the key and value from the json before delegating to the correct type adapter.

The consequence of this is that the models cannot use the subtype key property.

This is especially problematic if the developer intends to serialize and deserialize the same model.

[LachlanMcKee]

This issue has been resolved.