Drop trailing slash in URL to query routes

This one slipped through the tests, I think because the automagic handling of
trailing slashes by the net/http muxer.

With it, the command:

    $ kapow route list

fails with a 'Not Found'.

internal/client/route_list.go

@@ -8,6 +8,6 @@ import (
 
 // ListRoutes queries the kapow! instance for the routes that are registered
 func ListRoutes(host string, w io.Writer) error {
-	url := host + "/routes/"
+	url := host + "/routes"
 	return http.Get(url, "", nil, w)
 }