Fix #7 Slim 3.4 support

Author: mnapoli

src/config.php

@@ -22,13 +22,17 @@
     'settings.outputBuffering' => 'append',
     'settings.determineRouteBeforeAppMiddleware' => false,
     'settings.displayErrorDetails' => false,
+    'settings.addContentLengthHeader' => true,
+    'settings.routerCacheFile' => false,
 
     'settings' => [
         'httpVersion' => get('settings.httpVersion'),
         'responseChunkSize' => get('settings.responseChunkSize'),
         'outputBuffering' => get('settings.outputBuffering'),
         'determineRouteBeforeAppMiddleware' => get('settings.determineRouteBeforeAppMiddleware'),
         'displayErrorDetails' => get('settings.displayErrorDetails'),
+        'addContentLengthHeader' => get('settings.addContentLengthHeader'),
+        'routerCacheFile' => get('settings.routerCacheFile'),
     ],
 
     // Default Slim services