I had the same issue today. In my case it was caused by a corrupt version of the rx jar in my local maven repo.
I fixed it by deleting the rxjava folder inside .m2/io/reactivex. Then build your project again it should pull down the jar again which should fix the issue.
From:https://stackoverflow.com/questions/42624593/netflix-zuul-java-lang-classnotfoundexception-rx-functions-func1