missed 'extends curve'

src/extras/curves/ArcCurve.js

@@ -13,5 +13,4 @@ class ArcCurve extends EllipseCurve {
 
 }
 
-
 export { ArcCurve };

src/extras/curves/LineCurve.js

@@ -1,7 +1,7 @@
 import { Vector2 } from '../../math/Vector2.js';
 import { Curve } from '../core/Curve.js';
 
-class LineCurve {
+class LineCurve extends Curve {
 
 	constructor( v1, v2 ) {