Update to Scalr Signature miss-match response

Update to Scalr Signature miss-match response from ERROR to NIL. This is to resolve the issue with AND or OR Match rules

hook/hook.go

@@ -146,7 +146,7 @@ func CheckScalrSignature(headers map[string]interface{}, body []byte, signingKey
  	expectedSignature := hex.EncodeToString(mac.Sum(nil))
  
  	if !hmac.Equal([]byte(providedSignature), []byte(expectedSignature)) {
- 		return false, &SignatureError{providedSignature}
+ 		return false, nil
 	}
 
 	if !checkDate {