fix(Pico::loadPlugins): use require once to be able to reload Pico

lib/Pico.php

@@ -654,7 +654,7 @@ class Pico
     {
         // scope isolated require()
         $includeClosure = function ($pluginFile) {
-            require($pluginFile);
+            require_once($pluginFile);
         };
         if (PHP_VERSION_ID >= 50400) {
             $includeClosure = $includeClosure->bindTo(null);