Problem in migration from PSR-0 to PSR-4

I'm new here but I've been programming for more than 10 years in PHP and I'm programming Object Oriented in a short time. Doing some tests I saw that the PSR-0 is deprecated and then a project of mine that I am developing I decided to migrate to the PSR-4 there started the problem. at the time of running the application began to give the following error: Fatal error: Class 'PS \ Init \ Bootstrap' not found in E: \ Projects \ System \ App \ Init.php on line 6, where the file exists and worked on PSR-0.

I'm going to post my composer.json and my folder structure to see if I can fix this error otherwise I'll have to go back to the PSR-0.

-/Sistema
   - App
      - Clientes
         - Controllers
         - Models
         - Views
      - Init.php
   - public
      - .htaccess
      - index.php
   - vendor
      - PS
         - Init
            - Bootstrap.php 

composer.json

{
"name": "PortalSinos/Sistema",
"require": {
    "php": ">=5.3"
},

"minimum-stability": "alpha",
"authors": [
{
    "name": "Alexandro Zaleski",
    "email": "[email protected]"
}
],
"autoload": {
"psr-4": {
    "PS\": "vendor/",
    "App\": "App/"
}
},
"config":{
    "bin-dir": "bin"
}}

If you can help me figure out the error, I appreciate it.

Thanks.