error loading via https

I love your plugin, but it loads the pdf viewer hardcoded via http. Since my webpage is https only, there is an error in console. If you change line 82 from:

$s_pdf_doc_viewer = 'https://docs.google.com/gview?embedded=true&url=';

to:

$s_pdf_doc_viewer = '//docs.google.com/gview?embedded=true&url=';

it would load over http or https without any problem.