Revert what might be the reason the site doesn't seem to be generating nightly

A brief, HackNight test made this look like a good idea, but I think
it's been keeping the site from generating since the fix I used only
works when the command generating the site is run from the directory of
the Rakefile.

This reverts commit 19fbc74e45910b42178a527728d98ce52ac82d37.

I think I should have instead interpolated `File.expand_path File.dirname(__FILE__)` into the `#require` strings as in https://github.com/scooter-dangle/bmoreonrails/tree/require-compatibility

(I held off generating a pull request for that instead since getting the cron job running seems more important than mucking about anymore with compatibility.)

Sorry for breaking the Rakefile! / Thanks for the good reason to look up the `#require` docs!