Fixed one forgotten variable rename update

* `iss` was changed to `issuer` in 6baf47c764f. Updates were
  made on line 74 (related to line 80), but the call in the
  `random` function was forgotten. This causes an error becuase
  the DNS library is not able to resolve a host of 'undefined'.
Merge pull request #4 from tomkersten/Forgotten_Variable_Update

Fixed one forgotten variable rename update