Update stream_file_builder.go

Changed width of columns in stream files so they correctly show dates in default style

stream_file_builder.go

@@ -162,6 +162,7 @@ func (sb *StreamFileBuilder) AddSheetWithStyle(name string, cells []StreamCell)
 	// Set default column types based on the cel types in the first row
 	for i, cell := range cells {
 		sheet.Cols[i].SetType(cell.cellType)
+		sheet.Cols[i].Width = 11
 	}
 	return nil
 }