Fix some panic information when multiple similar wildcards conflict

[jummyliu]

  tree := &node{}
  tree.addRoute("/whose/:users/:name", fakeHandler("/whose/:users/:name"))
  tree.addRoute("/whose/:users/:user", fakeHandler("/whose/:users/:user")) // Wildcard Conflict panic

The second one will throw panic, but the information is not what I want (Maybe I don't completely understand it, this route /whose/:name is not defined). It likes below:

':user' in new path '/whose/:users/:user' conflicts with existing wildcard ':name' in existing prefix '/whose/:name'

I think below information are better.

':user' in new path '/whose/:users/:user' conflicts with existing wildcard ':name' in existing prefix '/whose/:users/:name'

So I change it. :)