Enable sandbox plugin (#554)

Summary:
Removes a gatekeeper that shouldn't be there.
Reported in https://github.com/facebook/flipper/issues/535
Pull Request resolved: https://github.com/facebook/flipper/pull/554

Reviewed By: danielbuechele

Differential Revision: D17502725

Pulled By: jknoxville

fbshipit-source-id: 1865db3f5c8cd81b0ec747687d0a7312e5f2332b

src/plugins/sandbox/package.json

@@ -5,7 +5,6 @@
   "main": "index.js",
   "license": "MIT",
   "keywords": ["flipper-plugin"],
-  "gatekeeper": "sonar_sandbox_plugin",
   "icon": "translate",
   "bugs": {
     "email": "edoardo@fb.com"