SignatureSystem properly failback on this an other possible errors

```
  microservice:validate Validate:SignatureSystem +0ms
crypto.js:117
  this._handle.init(hmac, toBuf(key));
               ^

Error: Unknown message digest
    at new Hmac (crypto.js:117:16)
    at Object.Hmac (crypto.js:115:12)
    at signature (node_modules/@microservice-framework/microservice/includes/signature.js:9:17)
   
```