title: Formatting [] array like params Rails
body: <p>here my view code:</p>
  
  <pre><code>- @categories.each do |c|
  %li.menu-drop
  = check_box_tag "categories[]", c.id
  .tipo-infor
      = c.title
  </code></pre>
  
  <p>when i submit this form, it generate this url:</p>
  
  <pre><code>http://0.0.0.0:3000/buscar-projetos-com?utf8=%E2%9C%93&amp;categories%5B%5D=3&amp;categories%5B%5D=4&amp;commit=Pesquisar
  </code></pre>
  
  <p>my question is how to better display this url just like:</p>
  
  <pre><code>http://0.0.0.0:3000/buscar-projetos-com?categories=2,3,4,5
  </code></pre>