PDF preview broken on 2.1

Failing on demo:
http://demo.ckan.org/dataset/pdf-test/resource/5597e098-83bb-4ffd-835b-2e94688007b8

Working:
http://demo.offene-daten.me/dataset/pdf-test/resource/f725204e-297b-44dd-bd1f-69764e34618b

@vitorbaptista :
> Quickly looking into demo, it seems that pdfjs' minified version in https://github.com/okfn/ckan/blob/master/ckanext/pdfpreview/theme/public/vendor/pdfjs/pdf.min.js is broken. Looking in pdf.js' issues, it seems they had problems with minification already (https://github.com/mozilla/pdf.js/issues/2479). As our pdf.min.js version is 10 months old, while pdf.js is 2 months, I guess we should re-minify it.