Set Callback URL check to Case Insensitive

I had been having issues testing Twitter login when I set my namespace to something like this: 'NameSpaceName.auth0.com'. No errors, but the callback wasn't being called. After debugging, I found that in webView:shouldStartLoadWithRequest:navigationType: inside the Auth0WebViewController, the requestURLString was coming back all lowercase. 

Now that I'm starting to understand Auth0, I see that it's the return URL I set in the dashboard application settings. But in order to fool proof this for future users, I set the return URL check to case insensitive, in case there are capitals in the namespace from instantiating the auth client.