don't show previous build button for first job run

src/resources/tpl/run.html

@@ -4,7 +4,7 @@
  <h3 style="float:left"><img class="spin" src="/progress.png" ng-hide="job.result"><span ng-bind-html="runIcon(job.result)"></span> {{name}} #{{num}}</h3>
  <nav class="pull-left">
   <ul class="pagination" style="margin:15px 20px">
-   <li><a href="jobs/{{name}}/{{num-1}}">&laquo;</a></li>
+   <li ng-show="num > 1"><a href="jobs/{{name}}/{{num-1}}">&laquo;</a></li>
    <li ng-show="latestNum > num"><a ng-href="jobs/{{name}}/{{num+1}}">&raquo;</a></li>
   </ul>
  </nav>