Make jsonrpc protocol version field in Response as Option

[gnapoli23]

Problem

JSON-RPC 2.0 specification does not require jsonrpc version in responses as a mandatory field: JSON-RPC 2.0 Spec
For RPC servers that put this value to null, the lib can't deserialize this responses, 'cause it actually requires this field to be present

Solution

Make jsonrpc field in Response as Option.

Fixes #1045

[gnapoli23]

Btw don't know why the CI failed for last commit but I tested in local and everything goes well. Maybe a re-run of the CI can be a better shot :)

[niklasad1]

Btw don't know why the CI failed for last commit but I tested in local and everything goes well. Maybe a re-run of the CI can be a better shot :)

Don't worry the gitlab pipeline has an old rustc version running, we will update it soon that's why it fails