Try using the following for the expression:
(DT_WSTR,10)(RIGHT("0" + (DT_STR, 2, 1252) DATEPART("mm" , DATEADD("D", 0 - (DATEPART("weekday", GETDATE()) % 7) , GETDATE())), 1) + "-" + RIGHT("0" + (DT_STR, 2, 1252) DATEPART("dd" , DATEADD("D", 0 - (DATEPART("weekday", GETDATE()) % 7) , GETDATE())), 2) + "-" + RIGHT("0" + (DT_STR, 4, 1252) DATEPART("yy" , DATEADD("D", 0 - (DATEPART("weekday", GETDATE()) % 7) , GETDATE())), 4))