title: Laravel Migration Change to Make a Column Nullable
body: <p>I created a migration with unsigned <code>user_id</code>. How can I edit <code>user_id</code> in a new migration to also make it <code>nullable()</code>?</p>
  
  <pre><code>Schema::create('throttle', function(Blueprint $table)
  {
      $table-&gt;increments('id');
      // this needs to also be nullable, how should the next migration be?
      $table-&gt;integer('user_id')-&gt;unsigned();
  }
  </code></pre>