rtiow: bump editions to 2021

rtiow/renderer/src/triangles.rs

@@ -20,7 +20,7 @@ where
     M: Material,
 {
     triangles: Vec<Triangle>,
-    bbox: Option<AABB>,
+    bbox: AABB,
     material: M,
 }
 
@@ -53,7 +53,7 @@ where
                 )
             },
         );
-        let bbox = Some(AABB::new(min, max));
+        let bbox = AABB::new(min, max);
         Triangles {
             triangles,
             bbox,
@@ -71,6 +71,6 @@ where
     }
 
     fn bounding_box(&self, _t_min: f32, _t_max: f32) -> Option<AABB> {
-        self.bbox
+        Some(self.bbox)
     }
 }