title: nth-of-type not working as needed
body: <p>I am doing responsive website. My HTML code is as given below:</p>
  
  <pre><code>&lt;h2&gt;Title&lt;/h2&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;h2&gt;Title&lt;/h2&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  </code></pre>
  
  <p>CSS is like this:</p>
  
  <pre><code>.column-5{width:18.4%; margin-right:2%;}
  .column-5:last-child{margin-right:0;}
  </code></pre>
  
  <p>and my JS like</p>
  
  <pre><code>$('.column_5:nth-of-type(5n+5)').addClass('last-child')
  </code></pre>
  
  <p>The output the above code currently produces is as follows:</p>
  
  <pre><code>&lt;h2&gt;Title&lt;/h2&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5 last-child"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;h2&gt;Title&lt;/h2&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5 last-child"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5 last-child"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  </code></pre>
  
  <p>However, what I am expecting/need is the below. Effectively, I need the <code>last-child</code> class to be added to every 5th consecutive element with the <code>column-5</code> class.</p>
  
  <pre><code>&lt;h2&gt;Title&lt;/h2&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5 last-child"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;h2&gt;Title&lt;/h2&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5 last-child"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5 last-child"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  &lt;div class="column-5"&gt;...&lt;/div&gt;
  </code></pre>
  
  <p>How can I achieve this?</p>