Have DateTimeWidget include the time zone in its type.

src/widgets/datetime.rs

@@ -22,7 +22,7 @@ pub struct TimeColor {
 
 impl DateTimeWidget<Local> {
     pub fn new(fmt: String) -> Self {
-        DateTimeWidget::tz(fmt, Local)
+        DateTimeWidget::<Local>::tz(fmt, Local)
     }
 }