chore(release): copies es6 index.js file into project root

This satisfies ionic optimization build

Author: stalniy

Diff for: .gitignore

@@ -33,6 +33,7 @@ bower_components
 # Compiled binary addons (http://nodejs.org/api/addons.html)
 build/Release
 dist/
+index.js
 
 # Dependency directories
 node_modules/

Diff for: package.json

@@ -36,7 +36,7 @@
     "test": "NODE_ENV=test nyc mocha spec/*.spec.js",
     "coverage.submit": "nyc report --reporter=lcov && codecov",
     "lint": "eslint -c .eslintrc src/",
-    "prerelease": "NODE_ENV=production npm run build && npm test",
+    "prerelease": "NODE_ENV=production npm run build && npm test && cp dist/es6/index.js .",
     "release": "standard-version"
   },
   "keywords": [