Increase uniqid entropy

While we don't have that many tokens in play at any one time, this will
increase the likelihood that the tokens are unique.

src/Guard.php

@@ -215,7 +215,7 @@ protected function createToken(): string
     public function generateToken(): array
     {
         // Generate new CSRF token
-        $name = uniqid($this->prefix);
+        $name = uniqid($this->prefix, true);
         $value = $this->createToken();
         $this->saveTokenToStorage($name, $value);