fix: Print more details on errors

Use a newer version of `nethsm_sdk_rs` which fixes the "serde
error" issue reported upstream: [#30].

Explicitly handle the response error and prints the content
that the NetHSM API returns, in case it is available.

[#30]: https://github.com/Nitrokey/nethsm-sdk-rs/issues/30

Fixes: #29


Signed-off-by: Wiktor Kwapisiewicz <wiktor@metacode.biz>