The library shouldn't alter PHP's default timezone

IMHO the fix for #70 should be reverted. It's not up to a library to try and fix the user's PHP environment in case their setup is broken and their date.timezone php.ini directive is not set.

The only result is to unexpectedly change the timezone whenever the library is used, setting it to UTC by default. Requiring the user to pass the correct timezone as a config variable doesn't seem to be a sane option either.