title: withoutOverlapping() is not working in Laravel Schedule
body: <pre><code>$schedule-&gt;call(function () 
          {
              error_log("Line Schedule 1:Start");
              //Send Email
              error_log("Line Schedule 1:End");
  
          })-&gt;everyFiveMinutes()-&gt;name('event_name:1')-&gt;withoutOverlapping();
  
  
          $schedule-&gt;call(function () 
          {
            error_log("Line Schedule 2:Start");
             //Send Email
            error_log("Line Schedule 2:End");
          })-&gt;everyFiveMinutes()-&gt;name('event_name:2')-&gt;withoutOverlapping();
          $schedule-&gt;call(function () 
          {
            error_log("Line Schedule 3:Start");
                //Send Email
            error_log("Line Schedule 3:End");
          })-&gt;everyFiveMinutes()-&gt;name('event_name:3')-&gt;withoutOverlapping();
  </code></pre>
  
  <p>i run these schulders using command php artisan schedule:run and i am running many instances in parallel. and my logs file says that schulder 2 is starting second time even its previous instance has not completed it yet .</p>
  
  <pre><code>[01-Jan-2016 11:30:08 UTC] Line Schedule 1:Start
  [01-Jan-2016 11:30:11 UTC] Line Schedule 2:Start
  [01-Jan-2016 11:30:13 UTC] Line Schedule 3:Start
  [01-Jan-2016 11:30:15 UTC] Line Schedule 1:End
  [01-Jan-2016 11:30:15 UTC] Line Schedule 2:Start
  [01-Jan-2016 11:30:17 UTC] Line Schedule 2:End
  [01-Jan-2016 11:30:17 UTC] Line Schedule 3:Start
  [01-Jan-2016 11:30:19 UTC] Line Schedule 3:End
  [01-Jan-2016 11:30:21 UTC] Line Schedule 2:End
  [01-Jan-2016 11:30:21 UTC] Line Schedule 3:Start
  [01-Jan-2016 11:30:22 UTC] Line Schedule 3:End
  [01-Jan-2016 11:30:25 UTC] Line Schedule 3:End
  </code></pre>