StashBuilds: Use the trigger member when merging the PR

FindBugs detected correctly that it was unused.

Author: proski

src/main/java/stashpullrequestbuilder/stashpullrequestbuilder/StashBuilds.java

@@ -94,8 +94,7 @@ public void onCompleted(AbstractBuild<?, ?> build, TaskListener listener) {
         duration);
 
     // Merge PR
-    StashBuildTrigger trig = StashBuildTrigger.getTrigger(build.getProject());
-    if (trig.getMergeOnSuccess() && build.getResult() == Result.SUCCESS) {
+    if (trigger.getMergeOnSuccess() && build.getResult() == Result.SUCCESS) {
       boolean mergeStat =
           repository.mergePullRequest(cause.getPullRequestId(), cause.getPullRequestVersion());
       if (mergeStat == true) {