Update version, changelog

Since the bugfix introduced in #19 didn't include any update to the version and changelog, I'm doing this here.
I wonder if this could be more succinct. We could also make it more relevant to the user; I think it would suffice to say that we weren't retrieving fixture parameters correctly in cases where the networks did not already exist.

The detail about classes is not so important for someone reading the CHANGELOG; if they want to see how we fixed it they can always look at the commit history.