Fix direct routes

There's a bug in the code for direct routes that are not over multiple hops.
min-route expects a collection so we should always return a collection.

This way it works for both direct and indirect routes:

(find-path (grouped-routes routes) :paris :london)
;; => {:cost 236, :best [:paris :london]}
(find-path (grouped-routes routes) :paris :budapest)
;; => {:cost 251, :best [:paris :milan :vienna :budapest]}

Author: transducer

Chapter06/Exercise6.07/train_routes.clj

@@ -55,7 +55,7 @@
       (= position destination) path
 
       (get-in route-lookup [position destination])
-      (conj path destination)
+      [(conj path destination)]
 
       :otherwise-we-search
       (let [path-set (set path)