L9 MCMC notebook pandas.tools

I am a student from CS5340 this semester.

The pandas.tools module was removed in pandas version 0.23.0, so you cannot import autocorrelation_plot from pandas.tools.plotting. Instead, you can use the following import statement:

```python
from pandas.plotting import autocorrelation_plot
```

The pandas version you use when you developed this repo is outdated, maybe this is better