Try to get number from issue or pull request

lib/payload.js

@@ -7,7 +7,7 @@ module.exports = class Payload {
     return Object.assign(object, {
       owner: this.repository.owner.login,
       repo: this.repository.name,
-      number: this.issue.number
+      number: (this.issue || this.pull_request || this).number
     });
   }
 };