Move session cookie name config right before session start.

As suggested by @merumelu in b1d3172f89

api/config.php

@@ -1,5 +1,2 @@
 <?php
-
-session_name('assetlib-csrf');
-
 ?>

src/dependencies.php

@@ -60,6 +60,7 @@ $container['utils'] = function ($c) {
 
 // csrf guard
 $container['csrf'] = function ($c) {
+  session_name('assetlib-csrf');
   session_start();
   return new \Slim\Csrf\Guard;
 };