Updated wkhtmltopdf to version 0.12.1

Updated wkhtmltopdf binaries to 0.12.1 to include bug fixes from them, particularly the fix for [Windows Server 2008 R2 x64](https://github.com/wkhtmltopdf/wkhtmltopdf/issues/1512) which can be seen included in their [release notes](https://github.com/wkhtmltopdf/wkhtmltopdf/releases/tag/0.12.1). Tests are passing as they were when I pulled the code down, and my tests seem to work fine. Anything else I should check or do?