fix DataGridCell issue

fixes

System.Windows.Data Error: 4 : Cannot find source for binding with
reference 'RelativeSource FindAncestor,
AncestorType='System.Windows.Controls.DataGridRow', AncestorLevel='1''.
BindingExpression:Path=Foreground; DataItem=null; target element is
'DataGridCell' (Name=''); target property is 'Foreground' (type 'Brush')