Updated Rakefile :preview command to new Jekyll standards

jekyll --server --auto is deprecated and has been replaced with jekyll serve(r) -w(atch)

Author: kvannotten

Rakefile

@@ -98,7 +98,7 @@ end # task :page
 
 desc "Launch preview environment"
 task :preview do
-  system "jekyll --auto --server"
+  system "jekyll serve -w"
 end # task :preview
 
 # Public: Alias - Maintains backwards compatability for theme switching.