title: Flexdashboard: dynamically change navbar title
body: <p>How can I dynamically change the navbar title from a R flexdashboard document. For instance I tried the code below to dynamically display when was the flexdashboard last updated.</p>
  <p>If possible, I am looking for a solution that doesn't rely on any external call.</p>
  <pre class="lang-r prettyprint-override"><code>---
  title: &quot;My title&quot;
  output: 
    flexdashboard::flex_dashboard:
      orientation: columns
      vertical_layout: fill
      navbar:
        - { title: `r paste0(&quot;Last updated at: &quot;, Sys.time())` }
  ---
  </code></pre>
  <p>But it returns an error:</p>
  <pre class="lang-r prettyprint-override"><code>Error in yaml::yaml.load(..., eval.expr = TRUE)
  </code></pre>