Bug 1219222 - Update bugherder link to point at the new Heroku instance

The old Stackato PaaS link 404s, so point at the Heroku instance's
herokuapp.com domain whilst we wait for the certificate/DNS to be set up
for it at bugherder.mozilla.org.

ui/partials/main/thActionButton.html

@@ -10,7 +10,7 @@
   <!-- Menu contents -->
   <ul class="dropdown-menu pull-right">
     <li><a target="_blank" ignore-job-clear-on-click
-           href="https://mcmerge.paas.allizom.org/?cset={{::resultset.revision}}&amp;tree={{::repoName}}"
+           href="https://mozilla-bugherder.herokuapp.com/?cset={{::resultset.revision}}&amp;tree={{::repoName}}"
            title="Use Bugherder to mark the bugs in this push">Mark with Bugherder</a></li>
     <li><a target="_blank" ignore-job-clear-on-click
            href="https://secure.pub.build.mozilla.org/buildapi/self-serve/{{::repoName}}/rev/{{::resultset.revision}}">BuildAPI</a></li>