Fixing bugs related to setting DateTime attributes

Fixing:
 - https://github.com/illuminate/database/commit/be7246d44f4667e27a196cbf91225f758b862004#L0R906
 - https://github.com/illuminate/database/commit/be7246d44f4667e27a196cbf91225f758b862004#L0R916
 - https://github.com/illuminate/database/commit/be7246d44f4667e27a196cbf91225f758b862004#L0R919