Bring back timestamps on JS bundles.

Timestamps are not present as of
dcc9b02.

This is a temporary workaround until the issue is properly fixed
upstream.

Also see documentcloud#268.

lib/jammit/helper.rb

@@ -30,7 +30,7 @@ def include_javascripts(*packages)
       html_safe packages.map {|pack|
         should_package? ? Jammit.asset_url(pack, :js) : Jammit.packager.individual_urls(pack.to_sym, :js)
       }.flatten.map {|pack|
-        "<script src=\"#{pack}\"></script>"
+        javascript_include_tag pack, options
       }.join("\n")
     end