have the http-kit instance returned as an HttpServer instance

this is more flexible, allowing a few http-kit functions to be called
against it (including one to stop http-kit), versus the alternate
return type which is just a simple function that can be called to stop
http-kit

this is ALSO what i thought i had done already, thus why the stop
function found below in this very same defstate is written to call
`http-kit/server-stop!` which won't actually work without setting
legacy-return-value? to false. oopsie! :-)

resources/leiningen/new/simple_web_service/src/root_ns/core.clj

@@ -171,7 +171,8 @@
                  (wrap-base #'handler)
                  {:port                 port
                   :ip                   bind
-                  :server-header nil})]
+                  :server-header        nil
+                  :legacy-return-value? false})]
     (log/info (format "Started HTTP server listening on %s:%d" bind port))
     server)
   :stop