title: Eloquent whereHasNot is missing
body: <p>I need to access eloquent's <code>whereHasNot</code> method (added here:<br>
  <a href="https://github.com/laravel/framework/commit/8f0cb08d8ebd157cbfe9fdebb54d2b71b0afaabd" rel="noreferrer">https://github.com/laravel/framework/commit/8f0cb08d8ebd157cbfe9fdebb54d2b71b0afaabd</a>)</p>
  
  <p>I have laravel/framework (v5.1.20) installed via composer.  However, the method does not exist in my <code>/Illuminate/Database/Eloquent/Builder.php</code> file. </p>
  
  <p>Here is what I have in composer.json</p>
  
  <pre><code>"laravel/framework": "5.1.*",
  </code></pre>
  
  <p>Am I missing somewhere here?  </p>
  
  <p>If I'm not able to add this via composer, how can I extend Eloquent within my app to add this method? </p>
  
  <p>Thanks!</p>