random errors when rendering pdf from html via POST

First - thank you so much for creating and working on this project.

I've deployed to Heroku. Most of the time pdf is generated, sometimes there is an error and entire node server crashes.

Here is the log: [url_to_pdf_api_error-01-25-2018.log](https://github.com/alvarcarto/url-to-pdf-api/files/1665510/url_to_pdf_api_error-01-25-2018.log)

Is there a good way to debug this problem? Currently it crashes around ~20% of the time. I was running on "hobby" initially, but had same results on 1x and 2x instance types.