title: How to control line size when working with autoplot() in the forecast package
body: <p>I am used to controlling line size in <code>geom_line(size=1)</code> in <code>ggplot</code>. I can't seem to find a way to control line size in the <code>autoplot()</code> function in the <code>forecast</code> package, For example, given the following code, how can I make the line size thicker?</p>
  
  <pre><code>&gt; library(forecast)
  &gt; d.arima &lt;- forecast::auto.arima(AirPassengers)
  &gt; autoplot(forecast::forecast(d.arima, h = 10))
  </code></pre>