newline at end of structure.sql file

a nitpick to make `db/structure.sql` more git-friendly avoiding the 'no newline at end of file" warnings:

![screen shot 2013-10-09 at 12 27 53 pm](https://f.cloud.github.com/assets/10403/1300364/f3c346fe-3110-11e3-9e0f-026f51c86b8e.png)