FIX: If forcing a refresh, don't return a onebox preview

app/controllers/onebox_controller.rb

@@ -6,10 +6,11 @@ class OneboxController < ApplicationController
   def show
     params.require(:user_id)
 
+    unless params[:refresh] == 'true'
       preview = Oneboxer.cached_preview(params[:url])
       preview.strip! if preview.present?
-
       return render(plain: preview) if preview.present?
+    end
 
     # only 1 outgoing preview per user
     return render(nothing: true, status: 429) if Oneboxer.is_previewing?(params[:user_id])