Add types to export

Author: jakearchibald

package.json

@@ -7,6 +7,7 @@
   "unpkg": "./dist/iife-compat.js",
   "exports": {
     ".": {
+      "types": "./dist/index.d.ts",
       "module": "./dist/index.js",
       "import": "./dist/index.js",
       "default": "./dist/index.cjs"