Change write in adapters to use the adapter based on class type

[LachlanMcKee]

There is an issue when using a base type in a AutoGsonAdapter class based around writing a field to json.

This is because at the moment the write will fetch the base type type adapter rather than using the type adapter of the inheriting type.

The fix is to change the write method to fetch the actual type adapter and leave the read alone.

[LachlanMcKee]

This has been released within 3.2.0