added custom provider for min username length for faker

faker/provider/CustomInternetProvider.php

@@ -0,0 +1,16 @@
+<?php
+namespace Faker\Provider;
+
+use Faker\Provider\Internet as BaseInternet;
+
+class CustomInternetProvider extends BaseInternet
+{
+    public function userNameWithMinLength($minLength = 6)
+    {
+        $username = $this->userName();
+        while (strlen($username) < $minLength) {
+            $username .= $this->randomNumber();
+        }
+        return $username;
+    }
+}