Multivariate sample data invalid?

### This issue is for a: (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [ ] feature request
- [x] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

### Minimal steps to reproduce
> The multivariate sample link at the bottom of this [readme](https://github.com/Azure-Samples/AnomalyDetector/tree/master/samples-multivariate) is invalid. Furthermore the actual zip file in the multivariate sample data looks like univariate data, what am I missing?

### Any log messages given by the failure
> N/A

### Expected/desired behavior
> Sample multivariate data

### OS and Version?
> N/A

### Versions
> N/A

### Mention any other details that might be useful

> ---------------------------------------------------------------
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