Remove json-loader dependency from React Redux

[agrcrobles]

Hi there,

json-loader is not required anymore because is supported by webpack 2 out of the box and could be safely removed from React Redux starter template.

When no loader has been configured for a JSON file, webpack will automatically try to load the JSON file with the json-loader either way.

It is related to webpack/webpack#3363

More info: https://webpack.js.org/guides/migrating/