REFACTOR: Replace `_.extend` with `Object.assign`

REFACTOR: Replace _.extend with Object.assign

diff --git a/app/assets/javascripts/admin/components/admin-web-hook-event.js b/app/assets/javascripts/admin/components/admin-web-hook-event.js
index 79011ce..49d689d 100644
--- a/app/assets/javascripts/admin/components/admin-web-hook-event.js
+++ b/app/assets/javascripts/admin/components/admin-web-hook-event.js
@@ -75,7 +75,7 @@ export default Component.extend({
       const expandDetailsKey = this.expandDetailsRequestKey;
 
       if (this.expandDetails !== expandDetailsKey) {
-        let headers = _.extend(
+        let headers = Object.assign(
           {
             "Request URL": this.get("model.request_url"),
             "Request method": "POST"
diff --git a/app/assets/javascripts/discourse/app/lib/formatter.js b/app/assets/javascripts/discourse/app/lib/formatter.js
index 529122c..e91e3fb 100644
--- a/app/assets/javascripts/discourse/app/lib/formatter.js
+++ b/app/assets/javascripts/discourse/app/lib/formatter.js
@@ -305,7 +305,7 @@ export function relativeAge(date, options) {
   } else if (format === "medium-with-ago") {
     return relativeAgeMedium(
       date,
-      _.extend(options, { format: "medium", leaveAgo: true })
+      Object.assign(options, { format: "medium", leaveAgo: true })
     );
   }
 

GitHub sha: 65f6a921

This commit appears in #10566 which was merged by eviltrout.