ghevent: add missing variants

So we don't see log messages that are literal pages long. Pulled from
here: https://developer.github.com/v3/activity/events/types/#pullrequestevent

ofborg/src/ghevent/pullrequestevent.rs

@@ -45,6 +45,9 @@ pub enum PullRequestAction {
     Opened,
     Edited,
     Closed,
+    ReadyForReview,
+    Locked,
+    Unlocked,
     Reopened,
     Synchronize,
 }