Update sphinx-rtd-theme from 0.4.3 to 0.5.0

Author: pyup-bot

docs/requirements.txt

@@ -1,6 +1,6 @@
 sphinx==1.8.5  # pyup: ignore
 sphinx-autoapi==1.4.0
-sphinx-rtd-theme==0.4.3
+sphinx-rtd-theme==0.5.0
 sphinx-tabs==1.1.13
 sphinx-prompt==1.1.0
 sphinx-version-warning==1.1.2