remove context generic

src/core/span.rs

@@ -5,8 +5,8 @@ pub struct Span {
     pub dir: Dir,
 }
 
-impl<Ctx: 'static> Widget<Ctx> for Span {
-    fn draw(&self, painter: &mut Painter<Ctx>) {
+impl Widget for Span {
+    fn draw(&self, painter: &mut Painter) {
         let total = self.sums();
         let mut start = UIScalar::min();
         for (child, length) in &self.children {