title: Can't update collection in Laravel eloquent
body: <p>There is a table with the following structure: (primary keys: user_id, record_id)</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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  <pre class="snippet-code-html lang-html prettyprint-override"><code>+---------+-----------+-------+
  | user_id | record_id | value |
  +---------+-----------+-------+
  |       1 |         1 |   100 |
  |       1 |         2 |   200 |
  |       2 |         1 |   300 |
  |       2 |         2 |   400 |
  +---------+-----------+-------+</code></pre>
  </div>
  </div>
  </p>
  <p>When i change <strong>value</strong> parameter over eloquent-query in my Controller like this:</p>
  <pre><code>$playerRecord = Test::where('user_id', '=', $player_id)-&gt;where('record_id', '=', '1')-&gt;first();
  $playerRecord-&gt;value = $user_value1;            
  $playerRecord-&gt;save();
  </code></pre>
  <p>I have an error: <a href="https://flareapp.io/share/47qg8ZEm#F49" rel="nofollow noreferrer">https://flareapp.io/share/47qg8ZEm#F49</a></p>
  <p>If I define only one primary key in the model, all records with this key are updated, despite the fact that I forced to update a specific record.</p>