Update sphinx-rtd-theme requirement from ~=1.1.0 to ~=3.0.1

Updates the requirements on [sphinx-rtd-theme](https://github.com/readthedocs/sphinx_rtd_theme) to permit the latest version.
- [Changelog](https://github.com/readthedocs/sphinx_rtd_theme/blob/master/docs/changelog.rst)
- [Commits](readthedocs/sphinx_rtd_theme@1.1.0...3.0.1)

---
updated-dependencies:
- dependency-name: sphinx-rtd-theme
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -142,7 +142,7 @@ Sphinx @ git+https://github.com/jenshnielsen/sphinx.git@fix_9884_5_3
 sphinx-favicon==0.2
 sphinx-issues~=3.0.1
 sphinx-jsonschema~=1.19.1
-sphinx-rtd-theme~=1.1.0
+sphinx-rtd-theme~=3.0.1
 sphinxcontrib-applehelp~=1.0.2
 sphinxcontrib-devhelp~=1.0.2
 sphinxcontrib-htmlhelp~=2.0.0