Add exists to users routes and fix endpoint.

app/controllers/users_controller.rb

@@ -86,7 +86,7 @@ class UsersController < ApplicationController
   end
 
   def exists
-    render json: { exists: !Namespace.where(name: params[:username]).nil? }
+    render json: { exists: Namespace.where(path: params[:username].downcase).any? }
   end
 
   private

config/routes/user.rb

@@ -33,5 +33,6 @@ scope(path: 'u/:username',
   get :projects
   get :contributed, as: :contributed_projects
   get :snippets
+  get :exists
   get '/', to: redirect('/%{username}')
 end