Set merged' action if merged' key is true

The GitHub API doesn't actually return `action = merged' when a PR
is merged; it just sets `pull_request.merged = true'.

From the Description field for the Action key:
https://developer.github.com/v3/activity/events/types/#pullrequestevent

Author: mcornella

server/index.js

@@ -133,6 +133,7 @@ function stripData(data){
         'created': data.created_at
       });
     }else if(data.type == 'PullRequestEvent'){
+      if (data.payload.pull_request.merged) data.payload.action = 'merged';
       stripedData.push({
         'id': data.id,
         'type': data.type,