Bump clj-time version to 0.8.0

Old clj-time version produces a nasty issue in case new version of the lib is used along with PigPen.
See https://github.com/clj-time/clj-time/issues/124

Some tests were failing due to the fact Clojure maps are not guaranteed to preserve kv pairs order.  Array- map are doing that. What structure behaviour to choose is up to the developer.