title: PaperTrail with STI appears to be storing wrong item_type
body: <p>According to the <a href="https://github.com/paper-trail-gem/paper_trail/blob/v10.3.1/README.md#5a-single-table-inheritance-sti" rel="nofollow noreferrer">docs</a> (and <a href="https://github.com/lorint/paper_trail/blob/master/spec/models/animal_spec.rb" rel="nofollow noreferrer">specs</a>) this STI setup below should work to log the history under my Agency subclass:</p>
  <pre><code>class Entity &lt; ApplicationRecord
  end
  
  class Agency &lt; Entity
    has_paper_trail
  end
  </code></pre>
  <p>however, the item_type on the history is being stored as Entity and the version history is not working as expected</p>
  <pre><code>pry&gt; Agency.create name:'My Org'
  =&gt; #&lt;Agency:0x00007fab7b003740
   id: 103,
   type: &quot;Agency&quot;,
   name: &quot;My Org&quot;
   ...
  pry&gt; Agency.last.version
    Agency Load (0.4ms)  SELECT &quot;entities&quot;.* FROM &quot;entities&quot; WHERE &quot;entities&quot;.&quot;type&quot; = $1 ORDER BY &quot;entities&quot;.&quot;id&quot; DESC LIMIT $2  [[&quot;type&quot;, &quot;Agency&quot;], [&quot;LIMIT&quot;, 1]]
  =&gt; nil
  pry&gt; Agency.last.versions
  PaperTrail::Version Load (0.4ms)  SELECT &quot;versions&quot;.* FROM &quot;versions&quot; WHERE &quot;versions&quot;.&quot;item_id&quot; = $1 AND &quot;versions&quot;.&quot;item_type&quot; = $2 ORDER BY &quot;versions&quot;.&quot;created_at&quot; ASC, &quot;versions&quot;.&quot;id&quot; ASC  [[&quot;item_id&quot;, 103], [&quot;item_type&quot;, &quot;Entity&quot;]]
  =&gt; [#&lt;PaperTrail::Version:0x00007fab72ec2118
    id: 222,
    item_type: &quot;Entity&quot;,
    item_id: 103,
    event: &quot;create&quot;,
    whodunnit: nil,
    object: nil,
    created_at: Mon, 29 Jun 2020 15:59:24 EDT -04:00,
    object_changes:
     {&quot;id&quot;=&gt;[nil, 103],
      &quot;name&quot;=&gt;[nil, &quot;My Org&quot;],
      &quot;slug&quot;=&gt;[nil, &quot;my-org&quot;],
      &quot;type&quot;=&gt;[nil, &quot;Agency&quot;],
      &quot;created_at&quot;=&gt;[nil, &quot;2020-06-29T15:59:24.344-04:00&quot;],
      &quot;updated_at&quot;=&gt;[nil, &quot;2020-06-29T15:59:24.344-04:00&quot;]}&gt;] 
  </code></pre>
  <p>Am I missing something or might this be a bug?</p>
  <p>Rails 6.0.3.2, PaperTrail 10.3.1</p>