Update interfaces/geometry.idl (#17991)

Source: https://github.com/tidoust/reffy-reports/blob/d6b9a8d/whatwg/idl/geometry.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/562428791
diff --git a/interfaces/geometry.idl b/interfaces/geometry.idl
index 5d5fe4f..1b83959 100644
--- a/interfaces/geometry.idl
+++ b/interfaces/geometry.idl
@@ -15,7 +15,7 @@
     readonly attribute unrestricted double z;
     readonly attribute unrestricted double w;
 
-    DOMPoint matrixTransform(optional DOMMatrixInit matrix);
+    [NewObject] DOMPoint matrixTransform(optional DOMMatrixInit matrix);
 
     [Default] object toJSON();
 };