Update composer puli suggest

Author: sagikazarmark

composer.json

@@ -21,7 +21,7 @@
         "henrikbjorn/phpspec-code-coverage" : "^1.0"
     },
     "suggest": {
-        "puli/composer-plugin": "Sets up Puli which is required for Discovery to work. Check http://docs.php-http.org/en/latest/discovery.html for more details.",
+        "puli/composer-plugin": "Sets up Puli which is recommended for Discovery to work. Check http://docs.php-http.org/en/latest/discovery.html for more details.",
         "php-http/message": "Allow to use Guzzle or Diactoros factories"
     },
     "autoload": {