Update sphinx-autoapi from 1.4.0 to 1.5.0

Author: pyup-bot

docs/requirements.txt

@@ -1,5 +1,5 @@
 sphinx==1.8.5  # pyup: ignore
-sphinx-autoapi==1.4.0
+sphinx-autoapi==1.5.0
 sphinx-rtd-theme==0.5.0
 sphinx-tabs==1.2.1
 sphinx-prompt==1.1.0