Add typescript definition to package json

Author: Eterion

package.json

@@ -3,8 +3,10 @@
   "version": "0.0.11",
   "description": "Embed javascript and css source inline when using the webpack dev server or middleware",
   "main": "index.js",
+  "types": "index.d.ts",
   "files": [
-    "index.js"
+    "index.js",
+    "index.d.ts"
   ],
   "scripts": {
     "prepublish": "npm run test",