Make PDFKit middleware set content disposition so that .pdf links are downloaded.

gistfile1.rb

require 'pdfkit'

class PDFKitMiddlewareDownload < PDFKit::Middleware
  def call(env)
    status, headers, response = super(env)

    if headers['Content-Type'] == 'application/pdf'
      headers['Content-Disposition'] = 'attachment'
    end

    [status, headers, response]
  end
end