React-SDK - 2.1.0

## [2.1.0] - July 8th, 2020
Upgrade `@optimizely/optimizely-sdk` to 4.1.0. See [@optimizely/optimizely-sdk Release 4.1.0](https://github.com/optimizely/javascript-sdk/releases/tag/v4.1.0) for more details.

## New Features
- Add support for JSON feature variables ([#53](https://github.com/optimizely/react-sdk/pull/53))

https://github.com/optimizely/react-sdk/releases/tag/2.1.0