Bump sphinx-rtd-theme from 0.5.1 to 0.5.2

Bumps [sphinx-rtd-theme](https://github.com/readthedocs/sphinx_rtd_theme) from 0.5.1 to 0.5.2.
- [Release notes](https://github.com/readthedocs/sphinx_rtd_theme/releases)
- [Changelog](https://github.com/readthedocs/sphinx_rtd_theme/blob/master/docs/changelog.rst)
- [Commits](readthedocs/sphinx_rtd_theme@0.5.1...0.5.2)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements/docs.txt

@@ -12,10 +12,10 @@ certifi==2020.12.5
     # via requests
 chardet==4.0.0
     # via requests
-colorama==0.4.4
-    # via sphinx
 docutils==0.16
-    # via sphinx
+    # via
+    #   sphinx
+    #   sphinx-rtd-theme
 idna==2.10
     # via requests
 imagesize==1.2.0
@@ -36,7 +36,7 @@ requests==2.25.1
     # via sphinx
 snowballstemmer==2.1.0
     # via sphinx
-sphinx-rtd-theme==0.5.1
+sphinx-rtd-theme==0.5.2
     # via -r requirements/docs.in
 sphinx==3.5.3
     # via sphinx-rtd-theme