Move doc requirements to doc

and update tox to later version

Change-Id: I4c07e622f2285513c86f168c15b375e62b5594ad
diff --git a/setup.cfg b/setup.cfg
index 0ccddef..2d91612 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -19,6 +19,8 @@
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
+
 
 [files]
 packages =