Update package.json

Correct webpack bundle error due to missing 'react-app' package.

package.json

@@ -49,6 +49,7 @@
     "postcss-pseudoelements": "^3.0.0",
     "postcss-selector-not": "^2.0.0",
     "react": "^15.0.2",
+    "react-app": "^1.0.0-alpha.3",
     "react-dom": "^15.0.2",
     "react-hot-loader": "^3.0.0-beta.2",
     "react-redux": "^4.4.5",