rename a bit

src/core/span.rs

@@ -43,7 +43,7 @@ impl Widget for Span {
         }
     }
 
-    fn size(&mut self, ctx: &mut SizeCtx) -> Vec2 {
+    fn get_size(&mut self, ctx: &mut SizeCtx) -> Vec2 {
         let total = self.setup(ctx);
         let axis = self.dir.axis;
         let dir_len = if total.ratio != 0.0 {