docs: Removed extraneous parens from article

<p>To ensure that your caching doesn't result in your app displaying stale data, be sure to extract the time at which the requested content was last updated, and when it expires, from within the HTTP response headers. This will allow you to determine when the associated content should be refreshed.</p>

<pre>long currentTime = System.currentTimeMillis());

<pre>long currentTime = System.currentTimeMillis();

HttpURLConnection conn = (HttpURLConnection) url.openConnection();