add exports field to support Node.js ESM

Author: PabloSzx

package.json

@@ -9,6 +9,20 @@
   "types": "index.d.ts",
   "sideEffects": false,
   "homepage": "https://github.com/graphql/graphql-js",
+  "exports": {
+    ".": {
+      "require": "./index.js",
+      "import": "./index.mjs"
+    },
+    "./package.json": {
+      "require": "./package.json",
+      "import": "./package.json"
+    },
+    "./*": {
+      "require": "./*.js",
+      "import": "./*.mjs"
+    }
+  },
   "bugs": {
     "url": "https://github.com/graphql/graphql-js/issues"
   },