Maintain "Start a discussion" button width on tags page

fixes flarum/core#1487

extensions/tags/less/forum.less

@@ -65,12 +65,13 @@
       &:after {
         display: none;
       }
+
+      > ul > li:first-child {
+        width: 190px;
+      }
     }
     .sideNavOffset {
       margin: 15px 0 0;
     }
   }
-  .TagsPage-nav .item-newDiscussion .Button {
-    width: auto;
-  }
 }