fix bug in issueBranchRef

src/hooks/issueBranchRef.js

@@ -14,7 +14,11 @@ module.exports = {
         log(`Try referencing ref ${ref} to issue`)
 
         const regex = /refs\/heads\/(feature|bugfix)\/ISS-(\d+)-/
-        const issueId = regex.exec(ref)[2]
+        const match = regex.exec(ref)
+        if(!match) {
+            return
+        }
+        const issueId = match[2]
 
         const path = `/repos/${repository.full_name}/issues/${issueId}`