Move tests/Fixture/* to tests/fixture/*

Signed-off-by: Nathanael Esayeas <[email protected]>

Remove CannotChangeTimezoneOfFrozenClockException.php

Signed-off-by: Nathanael Esayeas <[email protected]>

Update phpunit.xml.dist

Signed-off-by: Nathanael Esayeas <[email protected]>

Update SystemClockTest.php

Signed-off-by: Nathanael Esayeas <[email protected]>

Update README.md

Signed-off-by: Nathanael Esayeas <[email protected]>