Remove csrf from docs

This closes #712

Author: vinkla

docs/getting-started/lumen.md

@@ -29,7 +29,6 @@ $app->middleware([
 ```php
 $app->routeMiddleware([
     'check-authorization-params' => \LucaDegasperi\OAuth2Server\Middleware\CheckAuthCodeRequestMiddleware::class,
-    'csrf' => \Laravel\Lumen\Http\Middleware\VerifyCsrfToken::class,
     'oauth' => \LucaDegasperi\OAuth2Server\Middleware\OAuthMiddleware::class,
     'oauth-client' => \LucaDegasperi\OAuth2Server\Middleware\OAuthClientOwnerMiddleware::class,
     'oauth-user' => \LucaDegasperi\OAuth2Server\Middleware\OAuthUserOwnerMiddleware::class,