Disable page shrinking for pdf printing to create accurate output

PDFs are not rendered like PNG or other image formats by phantomjs because it
uses the printer functionality of Qt+Webkit. But Webkit uses some printer
"optimization" to save paper by shrinking the output. Such shrinking results in
too small content on a page.

https://github.com/ariya/phantomjs/issues/11590 ("page.paperSize is not
accurate for .pdf")