eager loading in production

see: https://github.com/discourse/discourse/commit/9d13c6b9315120df12bf1816cf5b4f71c5f7afaf

Heroku was breaking:
```
2013-11-26T23:26:05.947675+00:00 app[web.1]: config.eager_load is set to nil. Please update your config/environments/*.rb files accordingly:
2013-11-26T23:26:05.947675+00:00 app[web.1]:
2013-11-26T23:26:05.947675+00:00 app[web.1]:   * production - set it to true
2013-11-26T23:26:05.947675+00:00 app[web.1]:   * development - set it to false
2013-11-26T23:26:05.947675+00:00 app[web.1]:   * test - set it to false (unless you use a tool that preloads your test environment)
```