feat: add support for latest version of probot (#665)

Co-authored-by: Shine Lee <[email protected]>

Author: tenshiAMD

Diff for: lib/mergeable.js

@@ -94,7 +94,7 @@ class Mergeable {
 
   // version 2 of mergeable.
   flex (robot) {
-    robot.on('*', async pContext => {
+    robot.onAny(async pContext => {
       const context = new Context(pContext)
       logEventReceived(context)
       statEventReceived(context)