Javascript-SDK - 4.1.0-beta

## [4.1.0-beta] - June 16, 2020

### New Features
- Added support for JSON feature variables: new methods `getFeatureVariableJson` and `getAllFeatureVariables` ([#467](https://github.com/optimizely/javascript-sdk/pull/467), [#470](https://github.com/optimizely/javascript-sdk/pull/470))
- Added support for authenticated datafiles when running in Node.js. Pass `datafileAccessToken` within `datafileOptions` to request an authenticated datafile using the token ([#498](https://github.com/optimizely/javascript-sdk/pull/498), [#502](https://github.com/optimizely/javascript-sdk/pull/502)):
```js
const optimizelySDK = require('@optimizely/optimizely-sdk');
var optimizelyClientInstance = optimizely.createInstance({
sdkKey: '',
datafileOptions: {
datafileAccessToken: '',
}
});
```

### Bug fixes
- Fixed audience evaluation log level: changed from `INFO` to `DEBUG` ([#496](https://github.com/optimizely/javascript-sdk/pull/496))

https://github.com/optimizely/javascript-sdk/releases/tag/v4.1.0-beta