Add Content-Type application/json-rpc into Auto Unmarshaling support

[VadimKulagin]

I need to work with an API that provides JSON-RPC, which returns "Content-Type: application/json-rpc".

But this API client cannot automatically unmarshal a response with such a Content-Type.
This problem is similar to #134, #171, #92.

I think there are two solutions:

• rework the regular expression jsonCheck again;
• or make some parameter (ForceJSONUnmarshaling bool or ForcedResponceContentType string) that will force the Unmarshaling response into the correct format, regardless of the response Content-Type.

[jeevatkm]

@VadimKulagin Thank you for reporting an issue. Its better to add support via regex update.

[jeevatkm]

@VadimKulagin I have added support content-type application/json-rpc. You could point to master commit sha in your go.mod file and proceed.

I'm planning to release this enhancement in v1.11.0.

[jeevatkm]

Done 😄