Add JSON message when raising Error's

[allcentury]

As show in issue #38 when a 409 is received from provisioning a user, we currently raise a Validic::Errors::Conflict which is the correct behavior but we do not currently pass through the body of the message which has valuable context.

In this example, the body would be:

{
  "code": 409,
  "message": "Your organization is limited to 25 users"
}

I would think the error would be raised as:

raise Conflict, "Your organization is limited to 25 users"

Where that string is coming from the response body's 'message' key.

[diofeher]

👍 +1 on that.