Fix pipeline border variable

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/pages/pipelines.scss

@@ -20,7 +20,7 @@
 
   &:hover {
     background-color: $stage-hover-bg;
-    border: 1px solid $stage-hover-border;
+    border: 1px solid $$dropdown-toggle-active-border-color;
     color: $gl-text-color;
   }
 }