Replaced "Cache-Control: no-cache" with "Cache-Control: max-age=0"

Reference:
 -- http://blogs.msdn.com/b/ieinternals/archive/2009/10/02/internet-explorer-cannot-download-over-https-when-no-cache.aspx
 -- https://github.com/pdfcrowd/node-pdfcrowd/issues/4
added CHANGELOG
version bump to 1.1.1