title: Jekyll Liquid: Multiple calculations
body: <p>I'd like to display the previous year in my Jekyll posts. To get the current year, I just use:</p>
  
  <pre><code>We are in {{ site.time | date: '%Y' }} today
  </code></pre>
  
  <p>The question is, how do I get the previous year</p>
  
  <pre><code>We were in {{ site.time | date: '%Y' - 1 }}
  </code></pre>
  
  <p>That last statement doesn't work, hence the question.</p>