remove border and margin for reply buttons

src/client/styles/scss/_comment_growi.scss

@@ -100,11 +100,7 @@
   .btn.btn-comment-reply {
     width: 120px;
     margin-top: 0.5em;
-    margin-right: 15px;
-
-    border-top: none;
-    border-right: none;
-    border-left: none;
+    border: none;
   }
 
   // display cheatsheet for comment form only