Does not correctly handle verification_failed errors of API

[NikolaiGulatz]

The following response by the hunterio API is not properly handled in the gem:

{
  "errors": [
    {
      "id": "verification_failed",
      "code": 222,
      "details": "We failed to verify the email address for reasons outside of our control. We advise you to retry later."
    }
  ]
}

and leads to the following error since data is not present:

NoMethodError: undefined method `merge!' for nil:NilClass
  from hunter/email_verifier.rb:28:in `call_api'
  from hunter/email_verifier.rb:15:in `perform'
  from hunter/api.rb:31:in `email_verifier'