fix the typo

diff --git a/app/assets/javascripts/discourse/models/group.js.es6 b/app/assets/javascripts/discourse/models/group.js.es6
index 5639433..2b0081e 100644
--- a/app/assets/javascripts/discourse/models/group.js.es6
+++ b/app/assets/javascripts/discourse/models/group.js.es6
@@ -139,7 +139,7 @@ const Group = RestModel.extend({
 
   @computed("visibility_level")
   isPrivate(visibilityLevel) {
-    return visibility_level > 1;
+    return visibilityLevel > 1;
   },
 
   @observes("isPrivate", "canEveryoneMention")

GitHub sha: f0f6b715