title: Jenkins GitHub Pull Request Builder is being triggered by comments that don't match trigger phrase
body: <p>I have a repo that has three distinct "apps". Each app has a build job on Jenkins, they can all be triggered by a separate trigger phrase on a GitHub PR:
  <code>jenkins build app1</code>
  <code>jenkins build app2</code>
  <code>jenkins build app3</code></p>
  
  <p>Also, I have configured the trigger phrase on the job only (The "test phrase" field is blank in Manage Jenkins > Configure System > GHPRB > Advanced).</p>
  
  <p>The problem that I'm having is that <em>any</em> comment on a PR will trigger <em>all three</em> of these builds. Does anybody know how to fix this? I've exhausted my resources and have no idea where to look next.</p>