(PE-3443) Fix refer-clojure typo in sync.clj

Fixed typo in sync.clj in the (:refer-clojure) argument to ns.  :exclute
is now :exclude and the prior warning about references from
puppetlabs.http.client.sync/get overriding clojure.core/get is now
suppressed.
Merge pull request #2 from camlow325/maint/master/PE-3443-fix-refer-clojure-typo

(PE-3443) Fix refer-clojure typo in sync.clj