DDF-383 Fix test that fails in some timezones (UTC+7 or more).

getInstance() with no arguments uses local timezone, so the check for day of
month will return 4 (instead of the expected 3) for some timezones.

If we getInstance with UTC timezone, it'll work reliably.
Merge branch 'ddf-383' of http://github.com/bradh/ddf-spatial into bradh-ddf-383