Fix formatting issue for docstrings without param list

Fixes bug occured in Ceilometer V2 API doc:
http://docs.openstack.org/developer/ceilometer/webapi/v2.html#capabilities

The patch adds a blank line before return type block to avoid formatting
issues like this:
https://bugs.launchpad.net/ceilometer/+bug/1293547
Merge pull request #13 from ildikov/master

Fix formatting issue for docstrings without param list