Update interfaces/webxr.idl

Source: https://github.com/tidoust/reffy-reports/blob/7e834bb/ed/idl/webxr.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/647581361
diff --git a/interfaces/webxr.idl b/interfaces/webxr.idl
index 0360309..6734f5c 100644
--- a/interfaces/webxr.idl
+++ b/interfaces/webxr.idl
@@ -4,10 +4,10 @@
 // Source: WebXR Device API (https://immersive-web.github.io/webxr/)
 
 partial interface Navigator {
-  [SecureContext, SameObject] readonly attribute XR xr;
+  [SecureContext, SameObject] readonly attribute XRSystem xr;
 };
 
-[SecureContext, Exposed=Window] interface XR : EventTarget {
+[SecureContext, Exposed=Window] interface XRSystem : EventTarget {
   // Methods
   Promise<boolean> isSessionSupported(XRSessionMode mode);
   [NewObject] Promise<XRSession> requestSession(XRSessionMode mode, optional XRSessionInit options = {});