Updating minimum sphinx version in setup.py

[bsipocz]

Fixes #210

I'm seeing the getLogger error message in our CI but then in setup.py the fact that it should work with 1.2.3 has sent me into some dead-ends.

    logger = logging.getLogger(__name__)
AttributeError: module 'sphinx.util.logging' has no attribute 'getLogger'

[rgommers]

Thanks @bsipocz. I just updated it to 1.6.5 to match our CI and have a full version number.

Waiting for a decision on gh-210, then I'll either put this or another fix in and release 0.9.1 later today.

[jnothman]

Thanks @bsipocz