fix: fixes issue with DATE and timezone conversion

[kloostermanw]

This pull request fixes a DATE issue with timezone conversion.

for example this test was failing

    /**
     * Ensures setting DOB from a \DateTime (UTC) stores a date-only value and returns string when requested.
     *
     * Expectation: getDateOfBirth() returns '1980-01-01' as a string.
     */
    public function testSetsDateOfBirthFromDateTimeAndReturnsString()
    {
        $this->setupTestDatabase();

        $objEmployee = $this->getEmployeeCwJules();
        $objDateTime = new \DateTime('1980-01-01', new \DateTimeZone('UTC'));
        $objEmployee->setDateOfBirth($objDateTime);
        $objEmployee->save();

        $this->assertEquals('1980-01-01', $objEmployee->getDateOfBirth());
    }

closes #20