Avoid nasty surprises when deploying to a server west of you.

Creating a new post with the rake task now includes the time zone offset
so that when you write a post in GMT +2, then deploy it to your
production server in GMT -7, you don’t scratch your head wondering what
happened to your post.

Unfortunately, it might still happen that your file is named one day
differently than your post’s creation instant. I didn’t want to try to
fiddle with that. This seems to work well enough.