chore(package): explicitly declare js module type (#592)

Author: Fdawgs

Diff for: package.json

@@ -2,6 +2,8 @@
   "name": "eslint-plugin-promise",
   "version": "7.2.1",
   "description": "Enforce best practices for JavaScript promises",
+  "main": "index.js",
+  "type": "commonjs",
   "keywords": [
     "eslint",
     "eslintplugin",