Fix Sphinx docs

[kevinsung]

The documentation site is not rendering properly, even though it looks fine when viewing locally.

Console output:

Loading failed for the <script> with source “https://qiskit-community.github.io/qiskit-quimb/_static/documentation_options.js?v=1ffe7161”. [qiskit-quimb:374:65](https://qiskit-community.github.io/qiskit-quimb/)
Loading failed for the <script> with source “https://qiskit-community.github.io/qiskit-quimb/_static/doctools.js?v=9bcbadda”. [qiskit-quimb:375:50](https://qiskit-community.github.io/qiskit-quimb/)
Loading failed for the <script> with source “https://qiskit-community.github.io/qiskit-quimb/_static/sphinx_highlight.js?v=dc90522c”. [qiskit-quimb:376:58](https://qiskit-community.github.io/qiskit-quimb/)
Loading failed for the <script> with source “https://qiskit-community.github.io/qiskit-quimb/_static/scripts/furo.js?v=5fa4622c”.