Support Sprockets 3

[rmosolgo]

I just don't get why assets[logical_path].to_s fails in the gem code, but it works in the console!

~/code/react-rails-hot-loader/test/dummy $ rails c test
Loading test environment (Rails 4.2.2)
irb(main):001:0> puts Rails.application.assets["test_asset_1.js"].to_s
var testAsset1 = function () {
  return React.createElement(
    "span",
    null,
    "test asset 1"
  );
};

[rmosolgo]

Oh wait!

irb(main):002:0> puts Rails.application.assets["test_asset_1.js.jsx"].to_s
var testAsset1 = function () {
  return <span>test asset 1</span>;
};

Don't use .js.jsx !!!