Update doc theme to the latest (#2679)

Summary:
To follow the change related to Linux Foundation movement.

(we are still pinning the theme version so that our customization does not break randomly.)

Pull Request resolved: https://github.com/pytorch/audio/pull/2679

Reviewed By: carolineechen

Differential Revision: D39531566

Pulled By: mthrok

fbshipit-source-id: 64353577d05f9dbda00dd9d10b9ebcedddfdce5b

docs/requirements.txt

@@ -7,7 +7,7 @@ pyparsing<3,>=2.0.2
 # locations are working as expected.
 # - source/_templates/layout.html
 # - source/_static/css/custom.css
--e git+https://github.com/pytorch/pytorch_sphinx_theme.git@b4d0005#egg=pytorch_sphinx_theme
+-e git+https://github.com/pytorch/pytorch_sphinx_theme.git@cece053#egg=pytorch_sphinx_theme
 sphinx==3.5.4
 sphinxcontrib.katex==0.8.6
 sphinxcontrib.bibtex==2.4.2