Switch BitBucket code to always use the latest commit

Before this change, we'd use the first commit, which could be incorrect if there are multiple commits in a single push

Fixes #99

endpoints/trigger.py

@@ -516,7 +516,7 @@ class BitbucketBuildTrigger(BuildTriggerHandler):
       raise SkipRequestException()
 
     # Check if this build should be skipped by commit message.
-    commit = payload['commits'][0]
+    commit = payload['commits'][-1]
     commit_message = commit['message']
     if should_skip_commit(commit_message):
       logger.debug('Skipping BitBucket request due to commit message request')