Always recompile assets on build, fix for dependency issue

Assets weren't being recompiled when a file they depend on change, this was most evident with changing the `single_page.haml` and all the other pages wouldn't recompile.

This happens because the Rake File task will only execute if the target file either doesn't exist or its timestamp is older than the source file. This means the task won't execute if you change the layout without changing each file that uses it.

This change recompiles all the files every time a build is run. Obviously this is less than ideal, but without some kind of dependency graph it'll be difficult to conditionally compile things.