Align MqttJs "correlationData" field type with MqttNet

[sseiber]

This issue is for a: (mark with an x)

- [X] bug report -> please search issues before submitting
- [ ] feature request
- [ ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)

Minimal steps to reproduce

The MqttJs correlationData field is typed as a binary and I assumed it was of type Buffer in NodeJS.

Expected/desired behavior

Align the TypeScript sample Command use of correlationData to match the same data type/format that is being used in the MqttNet samples.

Language

TypeScript