[ZD#678967] double escape email

#bug

We need to encode the email in case it has a '+'.

/cc @maximeprades 

REFERENCES:

- [[ZD#678967] Highrise App/Integration errors and strange behaviour ](https://support.zendesk.com/agent/#/tickets/678967)
- [[APPS-1594] fix params encoding issue](https://zendesk.atlassian.net/browse/APPS-1594)