fix: update package.json to allow webpack bundling

Author: sis0k0

package.json

@@ -2,7 +2,7 @@
   "name": "nativescript-audio",
   "version": "2.1.3",
   "description": "NativeScript plugin to record and play audio.",
-  "main": "audio.js",
+  "main": "audio",
   "typings": "index.d.ts",
   "nativescript": {
     "platforms": {
@@ -55,4 +55,4 @@
     "tns-platform-declarations": "^2.3.0",
     "typescript": "^1.8.10"
   }
-}
+}