mileszs/wicked_pdf

## Issue description

## Expected or desired behavior

## System specifications

wicked_pdf gem version (output of `cat Gemfile.lock | grep wicked_pdf`):

wkhtmltopdf version (output of `wkhtmltopdf --version`):

whtmltopdf [provider gem](https://rubygems.org/search?utf8=%E2%9C%93&query=wkhtmltopdf) and version if one is used:

platform/distribution and version (e.g. Windows 10 / Ubuntu 16.04 / Heroku cedar):