Broken link in `examples/generalized_linear_models/multilevel_modeling.ipynb`

**Notebook title**:
`examples/generalized_linear_models/multilevel_modeling.ipynb`

**Notebook url**:
https://www.pymc.io/projects/examples/en/latest/generalized_linear_models/multilevel_modeling.html#multilevel-and-hierarchical-models

## Issue description
The links to external images are broken.
