Error saving token

...sometimes she gets an array
![image](https://user-images.githubusercontent.com/4215276/59840617-e775de00-937c-11e9-9cb8-4aab4c96b2db.png)

_Originally posted by @mrShturman in https://github.com/sendpulse/sendpulse-rest-api-node.js/issues/19#issuecomment-503963837_