Add files to package.json

closes jhiesey#2

Author: jimmywarting

package.json

@@ -9,6 +9,7 @@
     "test-browser": "airtap --loopback airtap.local -- test.js",
     "test-browser-local": "airtap --no-instrument --local 8080 -- test.js"
   },
+  "files": ["index.js"],
   "repository": {
     "type": "git",
     "url": "git://github.com/jhiesey/to-arraybuffer.git"