Expose the zoomFactor

The zoomFactor is an important factor when rendering the webpage. Please expose it:)

Author: Cosmo

lib/scripts/pdf_a4_portrait.js

@@ -35,6 +35,7 @@ var page = webpage.create()
 
 if (options.httpHeaders) page.customHeaders = options.httpHeaders
 if (options.viewportSize) page.viewportSize = options.viewportSize
+if (options.zoomFactor) page.zoomFactor = options.zoomFactor
 if (options.base) page.setContent(json.html, options.base)
 else page.setContent(json.html, null)