Update UnitOfWork.php

For datetime objects the comparison doesn't work ex:
 array (size=2)
      0 => 
        object(DateTime)[990]
          public 'date' => string '2007-10-25 00:00:00' (length=19)
          public 'timezone_type' => int 3
          public 'timezone' => string 'Europe/Luxembourg' (length=17)
      1 => 
        object(DateTime)[1876]
          public 'date' => string '2007-10-25 00:00:00' (length=19)
          public 'timezone_type' => int 3
          public 'timezone' => string 'Europe/Luxembourg' (length=17)

it's the same date but the scrict comparison make the original value is different of the actual value.