Javascript-SDK - 1.5.0

* Bump optimizely-server-sdk to version 1.4.0, which includes:
- Add support for numeric metrics.
- Add getForcedVariation and setForcedVariation methods for client-side variation setting
- Bug fix for filtering out null attribute and event tag values

https://github.com/optimizely/javascript-sdk/releases/tag/v1.5.0