[storage] update get_object requests to use excon response_blocks

lib/fog/rackspace/requests/storage/get_object.rb

@@ -21,7 +21,7 @@ module Fog
             :expects  => 200,
             :method   => 'GET',
             :path     => "#{Fog::Rackspace.escape(container)}/#{Fog::Rackspace.escape(object)}"
-          }, false))
+          }), false)
         end
 
       end