Plot environment

When I wanted to run the code and see the plots for D/D/1/K 
I encountered with 
```sh
FigureCanvasAgg is non-interactive, and thus cannot be shown
  plt.show()
``` 

To resolve this error, I had to add a few lines in the `src/plots.py` as follows: 

```python
import matplotlib
matplotlib.use('Qt5Agg')
``` 

