build: add main entry

Author: z0al

package.json

@@ -6,6 +6,7 @@
 	"license": "MIT",
 	"repository": "https://github.com/ahmed-taj/commitlint-bot.git",
 	"keywords": ["validate", "commit", "pr", "conventional", "git", "probot-app"],
+	"main": "index.js",
 	"scripts": {
 		"now": "now",
 		"now-start": "PRIVATE_KEY=$(echo $PRIVATE_KEY | base64 -d) npm start",