code: def update(self, friendly_name=values.unset, certificate=values.unset,
                 private_key=values.unset, sandbox=values.unset, api_key=values.unset,
                 secret=values.unset):
          
          data = values.of({
              'FriendlyName': friendly_name,
              'Certificate': certificate,
              'PrivateKey': private_key,
              'Sandbox': sandbox,
              'ApiKey': api_key,
              'Secret': secret,
          })
  
          payload = self._version.update(
              'POST',
              self._uri,
              data=data,
          )
  
          return CredentialInstance(self._version, payload, sid=self._solution['sid'], )
docs: Update the CredentialInstance
  
          :param unicode friendly_name: A string to describe the resource
          :param unicode certificate: [APN only] The URL-encoded representation of the certificate
          :param unicode private_key: [APN only] URL-encoded representation of the private key
          :param bool sandbox: [APN only] Whether to send the credential to sandbox APNs
          :param unicode api_key: [GCM only] The `Server key` of your project from Firebase console under Settings / Cloud messaging
          :param unicode secret: [FCM only] The `Server key` of your project from Firebase console under Settings / Cloud messaging
  
          :returns: Updated CredentialInstance
          :rtype: twilio.rest.notify.v1.credential.CredentialInstance