Add scroll-animations reviewers

Antoine and Stephen have recently been added as editors of the spec
diff --git a/scroll-animations/META.yml b/scroll-animations/META.yml
index 0123b6b..20f3c7e 100644
--- a/scroll-animations/META.yml
+++ b/scroll-animations/META.yml
@@ -2,3 +2,5 @@
 suggested_reviewers:
   - birtles
   - theres-waldo
+  - graouts
+  - stephenmcgruer