Update deps to class-transformer 0.2.0

[Artur Kozak]

I recently updated to class-transformer 0.2.0, becuase I wanted to use the discriminator feature that they introduced. From my brief tests it looks like it still works with this package, but my use cases are not too complicated, so I can't say everything's ok :) Anyway, it may be worth releasing with updated deps, probably as v0.7 since it's theoretically a breaking change for class-transformer.

[Michał Lytek]

@quezak
Feel free to make a PR for that 😉

[Artur Kozak]

@19majkel94 there you go :)