Calculating difference between dates with amDifference filter
<p><strong><a href="https://plnkr.co/edit/xFJ8NF?p=preview" rel="nofollow">Plunker</a></strong></p>

<p>I have a questions about using the amDifference filter in angular-moment.</p>

<p>Currently I have it set up like this:</p>

<pre><code>{{order.shipDate | amDifference: null: 'days'}}
</code></pre>

<p>Which is calculating the difference between the ship date and the current date, but it is backwards with what I need if for. For example, if my shipDate was on 12/05/2015 it is currently showing '-81', but I would like for it to show '81'. So I guess something like this:</p>

<pre><code>{{currentDate | amDifference: order.shipDate: 'days'}}
</code></pre>

<p>I have already tried this:</p>

<pre><code>{{null | amDifference: order.shipDate: 'days'}}
</code></pre>

<p>Which didn't work. </p>

<p>So I guess I want to know:</p>

<ol>
<li>Am I using the right angular-moment filter?</li>
<li>If I can use this filter, how do I accomplish it?</li>
</ol>

<p>Thanks so much!</p>