Upgrade sphinxcontrib-pecanwsme to version 0.8

Version 8.0 fixes "make rst for method not using wmse"
We encountered this issue in Solum when we had a Controller with
exposed methods that were not using WSME and only Pecan, so I fixed
this bug in sphinxcontrib-pecansme (Github Pull Request link:
https://github.com/dreamhost/sphinxcontrib-pecanwsme/pull/15)

Change-Id: I115240de45091de421afd56f7e0f061b582df08b
Closes-Bug: #1311875