Set a default timezone

Without setting a default timezone, I got an error like:

```
Warning: strtotime(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EDT/-4.0/DST' instead in /Users/ryanfaerman/Documents/repos/Gitboard/gitboard.php on line 72
```