clojure.org links without trailing slash which breaks them

[ylebedeva]

The clojure.org routing supposedly had stopped accepting HTTP URLs similar to http://clojure.org/reducers/, although http://clojure.org/reducers is perfectly fine. Several links provided in the text are now broken and are routed to http://clojure.org/404 instead of an intended article. Those trailing slashes are removed in the PR.