Ruby-SDK - 3.1.0

## 3.1.0
May 3rd, 2019

### New Features:
- Introduced Decision notification listener to be able to record:
- Variation assignments for users activated in an experiment.
- Feature access for users.
- Feature variable value for users.

### Bug Fixes:
- Feature variable APIs return default variable value when featureEnabled property is false. ([#162](https://github.com/optimizely/ruby-sdk/pull/162))

### Deprecated:
- Activate notification listener is deprecated as of this release. Recommendation is to use the new Decision notification listener. Activate notification listener will be removed in the next major release.

https://github.com/optimizely/ruby-sdk/releases/tag/3.1.0