fix: some loaders want a main export

Author: reconbot

package.json

@@ -2,7 +2,8 @@
   "name": "graphql-lambda-subscriptions",
   "version": "0.0.0-development",
   "description": "Rollup your code and types for publishing",
-  "types": "dist/index.d.ts",
+  "types": "./dist/index.d.ts",
+  "main": "./dist/index.js",
   "exports": {
     "require": "./dist/index.js",
     "default": "./dist/index-esm.mjs"