404 error when launching server

[wang-boyu]

Describe the bug

mesa runserver results in 404 errors and the visualization is not running properly:

$ mesa runserver
Interface starting at http://127.0.0.1:8521
404 GET /static/external/bootstrap-slider-11.0.2/dist/css/bootstrap-slider.min.css (127.0.0.1) 4.28ms
404 GET /static/external/bootstrap-slider-11.0.2/dist/bootstrap-slider.min.js (127.0.0.1) 1.42ms

Expected behavior

$ mesa runserver
Interface starting at http://127.0.0.1:8521
Socket opened!
{"type":"reset"}

To Reproduce

Go to the Schelling example and install latest dependencies: python3 -m pip install -Ur requirements.txt

Additional context

It is likely introduced through #39. If mesa-viz-tornado is installed at its previous commit, the issue disappears:

python3 -m pip install git+https://github.com/projectmesa/mesa-viz-tornado.git@b4e9cae550a6ef1580dd906a5f9a1b8c51726aa8#egg=mesa-viz-tornado