Replace deprecated icon

Replace deprecated icon

diff --git a/assets/javascripts/discourse/initializers/extend-for-solved-button.js.es6 b/assets/javascripts/discourse/initializers/extend-for-solved-button.js.es6
index 7feb4f1..023fdb1 100644
--- a/assets/javascripts/discourse/initializers/extend-for-solved-button.js.es6
+++ b/assets/javascripts/discourse/initializers/extend-for-solved-button.js.es6
@@ -256,7 +256,7 @@ export default {
             openTag: "span",
             closeTag: "span",
             title: I18n.t("solved.has_no_accepted_answer"),
-            icon: "square-o"
+            icon: "far-square"
           });
         }
         return results;

GitHub sha: be6ecbf6