Bump the sphinx to 1.6.2 for lower-constraints.txt
Bump the sphinx to 1.6.2 for lower-constraints.txt

1. Package 'sphinx' is constrained to 1.6.5 which does not match the
minimum version specifier 1.6.2 in doc/requirements.txt[0]

[0]: refer to https://github.com/openstack/python-muranoclient/blob/master/doc/requirements.txt#L5

Change-Id: Ia15cc48ce020ff936185d6a94312e68c3c1603b3

openstack/python-muranoclient,openstack/python-muranoclient