downgrade corelogic to 0.8.4

Running "lein check" throws an exception:

Exception in thread "main" java.lang.RuntimeException: No such var: logic/defrel, compiling:(joy/logic/planets.clj:4:1)

According to the change log for core.logic, this function has been removed in 0.8.5.  

https://github.com/clojure/core.logic/blob/master/CHANGES.md#from-084-to-085

Downgrading to the previous version of core.logic allows this code to work.  Alternately, this guy fixed the examples to work with the newer version of core.logic:  
https://gist.github.com/gamma235/ed29f2e4a9a07471e965 

The second problem that "lein check" found was that unify.clj was not using the right namespace:

Exception in thread "main" java.io.FileNotFoundException: Could not locate joy/unify__init.class or joy/unify.clj on classpath: , compiling:(/private/var/folders/sh/b3xw_cn108nc1nh1zv2kxk680000gn/T/form-init3042446268059918296.clj:1:142)

Not sure what's up with the newline on line 149, I think it's a windows vs mac thing but doesn't affect anything functional.